μTorrent has changed significantly after its purchase by BitTorrent. However, it remains the most popular torrent client due to its small size and performance. Its advertising can get very annoying, but there is a way to disable it.
The way to do this is to disable the following settings in the Advanced tab of the Settings menu:
This should take care of some of those ads, although future changes to the uTorrent code may remove this fix.
Thanks to Lifehacker for the tip.