To configure notifications for sub-folders:

Select an Inbox folder (e.g. Social) from the slide-out window. From the overflow menu (i.e. the three dots in the upper-right corner) select Label Settings Toggle on "Label notifications" and configure to your heart's content. Rinse, repeat with all the other folders.

To not have to put up with this nonsense:

Go to your Gmail Inbox via the web. Click the gear icon in the upper-right and select "Configure Inbox." Uncheck all the sub-folders and click Save. PROFIT!!! Also, get all your mail notified like before since the Inbox will revert to the old style.

Gmail 4.5 was not giving notifications most of the time. I had manually downloaded the APK on Monday and it seemed to work fine, but on Tuesday I noticed I wasn't getting any notifications. I rolled back the update via System>Apps>Uninstall Updates and it updated through Play to 4.3.x or something. Wednesday, the 4.5 update rolled out to me in Play and I updated, but now it's acting the same way, only giving notifications about 20% of the time, if that. Not cool.After practicing some Google fu, I finally found out what was causing the notification problem, namely that if you have the new tabbed inbox folders set up on the web, ONLY the Primary folder has notifications turned on by default if you have notifications set. The Social, Promotions, Updates and Forums folders are turned OFF by default and have to be manually configured, both in turning them on AND setting a ringtone. AFAIK, there is no "Make folders use master notification setting" option.I'll give you one guess as to which method I used. This folder system would be better IMO if we could notify based on labels instead of categories chosen by Google. Have one ringtone for your Significant Other, another for work emails, etc.Hope this helps someone!