Gmail is now rendering PowerPoint slide decks as a playable slide show. I've found a few files it's choked on (seems to be graphic density but that's very unscientific data so YMMV). It's very fast and quite useful when it works. I get a lot of PPT files and this is a nice quick way to make a decision whether I need to D/L the file or just leave it in Gmail and reference it there as needed.
This has not shown up on the What's New in Gmail page so not sure if this has been rolled out everywhere. As I'm generally not at the front of the queue on Gmail's incremental feature rollouts, I'm guessing this is available in all accounts. In addition to increased file attachment sizes (now 20MB) and direct sign-up, I wonder if maybe, just maybe, that beta tag is coming down soon?
H/T to Steve Rubel for pointing this out via Twitter.