With the latest/mango update to Windows Phone 7 there are a couple of changes/improvements to note.
This is property still exists and is still not used for anything but it no longer needs to be set. (Even thought the examples on MSDN still show it being set.)
ImageStream / MaxImageSize
Previously this was a tiny 16kb and it made it impossible to show high quality images (of album artwork or packshots) at 358x358 (or 173x173) pixels.
This has been dramatically increased to a much more practical 75kb.
Disappointingly this still isn't clearly documented in MSDN and the page on How to: Integrate with the Music and Videos Hub for Windows Phone (only lists the physical image dimensions, not the size on disk) and we have to rely on an exception to know what the limit is:
Also disappointingly, that page doesn't allow for community content. :(
I'm sure there's a good reason that not every page supports community content but it would be nice if they did because I'd add some useful information there is I could. I suspect more people would read that there than this here.