By now, most iTunes users have already downloaded and installed iTunes 10. We've already given you the low-down on the biggest addition to the new version of iTunes—the Ping social network—but we also wanted to give our impressions on two "improvements" promised in the release notes: look-and-feel and performance. While we agree that iTunes is "faster and more responsive," we're not sold on the revised user interface.

"Enjoy performance improvements which make iTunes faster and more responsive"

Let's face it, performance is not iTunes' strong suit. I have a decent-sized library of some 6,700 tracks, for a total of 30GB of storage space—I can listen to music for nearly 51 days straight without ever hearing the same song twice. That is not a small music library, but it certainly doesn't compare to many people I know that complain that an iPod classic still isn't big enough to hold their library.

If music was all that iTunes had to manage, juggling those 6,700 tracks wouldn't be much trouble. But it also keeps track of movies, TV shows, music videos, ePub and PDF books, iPhoto libraries, iPods, iPhones, iPads, audio books, iTunes U content, podcasts, Internet radio stations, other local iTunes libraries on the network well, you get the idea. Apple has piled additional functionality on software that originally started life as a Mac OS 8 MP3 player to the point where it is practically bursting at its Carbon seams.

For those with large libraries hoping for a full Cocoa rewrite, this is not the iTunes update you've been looking for. But while iTunes 8 and 9 got progressively slower—it got to the point that switching to iTunes to skip a track or stop it to answer a phone call was a five to ten second trial of patience—Apple promised that iTunes 10 would offer faster performance.

After playing with the new version for the better part of a day, we can honestly say it is a little snappier. It certainly doesn't suffer from the unresponsive UI that plagued iTunes 9 on my aging original Core Duo MacBook. Specific genres and artists load instantly in the browser. Flipping through albums in Cover Flow seems especially fast. And the new list view with album art scrolls like butter.

We're not sure what Apple is using behind the scenes—it's certainly not Cocoa, and Apple didn't respond to our questions about what specific enhancements had been added. After using both iTunes 9 and iTunes 10 with Activity Monitor running, it does seem that iTunes is using more threads and may be using a little more (about 5 percent) CPU time than before. It's not more efficient, but it is perceptibly faster—at this point, it's a trade-off we can accept.

We still hope for a fully turbo-charged, block-using, GCD-enabled, Cocoa-fied version of iTunes with blazing performance. iTunes 10 isn't there yet, but the tweaks that are there are welcome.

"Explore many look-and-feel improvements throughout iTunes"

Now, iTunes 10's new "look-and-feel" is an entirely different matter. Immediately noticeable is the cringe-inducing vertically aligned window controls. Admittedly, it does save a few pixels of vertical space, since Apple got rid of the title bar entirely. But the Human Interface Guidelines are there for a reason—to provide users with a consistent paradigm for interacting with applications. The common wisdom is that you shouldn't break the HIG unless there is a compelling reason. In our opinion, a few pixels of vertical space isn't a compelling enough reason, especially considering all the comments we have heard from colleagues and readers who find it confusing.

Thankfully, you can get rid of this style with a hidden terminal command. Quit iTunes 10, and enter defaults write com.apple.iTunes full-window -1 in a Terminal prompt. Relaunch iTunes and—voilà!—the standard window controls return.

Another major change is that Apple has pretty much removed all the color from iTunes sidebar. In previous version of iTunes, the icons representing different media, playlists, and devices in the left-hand sidebar came in a range of colors. Now all the icons are subtle, monochromatic shadows of their former selves. All the shapes are distinctive enough for the most part, but the low-contrast grey makes it more difficult to find what you are looking for at a glance. Instead of thinking "green" for the iTunes Store or "purple" for Genius Mixes, you'll have to pay more attention to the shapes and text labels. It may be more visually "refined," but in our opinion usability is hurt.

Yet another questionable UI tweak is that all the buttons along the bottom of the main iTunes window have lost their button shape. Instead, they appear as a series of—you guessed it—grey shapes that give only a vague clue they clicking them might do something. The style is reminiscent of the tab bars used on iOS applications, except even there the active tab has a rectangular button shape around it, giving users a subtle clue that the other icons could be clicked to activate them. In its default state, none of the buttons are active—those that are get a nice blue highlight fill—and so a user would have to rely on curiosity and pop-up tool tips to figure out what the buttons do, once they figure out that they are buttons in the first place. It's not terrible once you get used to it, but new users might miss these buttons entirely.

There are a couple smaller changes that we are neutral about, and two that we like. Apple has changed the volume control to make it thicker, and it has a subtle machined aluminum look. Being bigger makes it easier to target, especially with a trackpad. Apple also changed how some of the top-level categories in the sidebar are collapsed. Instead of using standard disclosure triangles, rolling over these categories (like Genius or Playlist) will reveal a "show" or "hide" text button to the right. Clicking the text will show or hide the stuff underneath these headings, but double-clicking them works the same, and is easier in our opinion.

The two changes we do like, however, are the redesigned list view column headings, and the new list view with album art icons. The new column headings are larger, with more space above and below the heading text. This makes it easier to target using a trackpad while also being more visually appealing. The added list view with small album art icons is also a nice touch for those who think visually but have too many albums to rely strictly on the album art or Cover Flow views.

It will be some time before we know what impact Ping will have on the iTunes user base, or whether TV rentals will be compelling enough to get more users watching (we suspect they would be more appealing for users of the new Apple TV when it comes out next month). The new iTunes UI might leave a lot to be desired, but at least Apple has made some effort to improve the overall performance.

Perhaps iTunes 11 will finally be the version that sheds the last vestiges of Carbon cruft. Hopefully Apple engineers will also give at least a passing nod to the Human Interface Guidelines when designing its UI.