I am using Windows 10, Mist Wallet 0.7.2 which includes geth v1.3.6, a non-SSD hard drive and ethernet connection to 16Mbs modem.

I had incredibly slow syncing of the blockchain, even with 25 peers and was actually having to to quit and restart Mist just to download another few blocks. I had installed the Mist Wallet for Win64 from here, which also includes a CLI called geth. (nb. apparently x32 editions don't contain geth?)

I followed numerous different recommendations, however none worked until I deleted the blockchain data using geth and kicked the whole process off again.

Rather than using the Mist sync process, I removed the chaindata and then ran geth --fast :

Opened the cmd prompt

Navigated to the directory containing geth.exe and opened it

Copied the file path from the bar Explorer

Typed cd path/to/geth (replace path/to/geth with what you copied) and hit enter.

Typed geth removedb and hit enter.

Once the blockchain was removed, I ran geth --fast

This above is also described here.

The download has now got to block 500,000 in 30 minutes which had previously taken 3 days!

If you are on a Mac, you would do this...

Right click on the ethereum-wallet.app and select 'show package contents'

Open 'contents', then 'frameworks', then 'node', then 'geth' and voila.

Then you should right click on geth and select 'show info'.

Copy the location marked 'Where:'.

Open Terminal and type 'cd `

Then type: ./geth --fast

Other recommended changes to Windows I had performed were:

Ensuring my PC clock time was synchronised with internet time (it was accurate)

Manually setting the Windows page size as per: http://www.tomshardware.co.uk/forum/id-2813275/disk-usage-100.html

Disabled Superfetch

Specifically opened the Ethereum ports for TCP 30303 and UDP 30301 on my router as described here: Which TCP and UDP ports are required to run an Ethereum client?

Whether any of these contributed to it being much faster after the geth removedb I'm not sure, but each of those may well help you.

The complete download of 1,500,000 blocks finished after about 10 hours, so the blocks definitely appear to take longer to download the greater the block number, due to the increased number of transactions contained in each block.