One thing is that the viewer for photographs just got better. Super-large photos are now resized automatically so they display at a good size for computer screens, and there's a navigation link to click through all the photos on a page without closing and opening the windows individually. A little thing, but a welcome improvement.
Podcast RSS feeds can now be subscribed to directly in iTunes (including videos!). This is pretty cool, actually. If you drag some audio and/or video files onto a Bubbler page and click the "RSS Feed" box in web settings, you are now podcasting, and people can subscribe to your podcast directly from iTunes (Advanced menu).
Another is that the "URL" field is no longer required when posting comments. This seemed to confuse some people who don't have blogs or web sites of their own, so now it's an optional field instead of a required field. A little thing, but important.
The Files list used to also include Photos. It doesn't now; it lists the "other" files that aren't photos.
The elves are always working here at Five Across, and although you don't always see the changes, things are always getting better, and faster.