You can now export JPG image sequences in addition to PNG image sequences. Use the dropdown in the Render dialog. This is good news if you're exporting sequences for use on the web.
You can now adjust the compression factor when exporting a JPG image sequence
Improvements
PNG Sequence is now called Image Sequence
Image sequence rendering now counts its frames from 0 instead of 1
Image sequence rendering now pads its counter to 4 digits, e.g. 0001
Image sequence rendering now defaults to extra high quality
Image sequence rendering now outputs web-friendly filenames without spaces and upper-case characters