I rarely look forward to new releases of products because it usually means I get to spend weeks trying to do a diff and merge with any customizations I’ve created: ie, more work for me. But I have to admit, I’m pretty excited to see how WP re-did their media management. Being used to hardcore/expensive content management systems, I always found how WP handles media to be lacking. So we’ll see what they’ve done and how better it’ll make your life.
The only pitfall I can see would involve themes/plugins. I’m sure the major players out there (woothemes included) got exclusive previews and could prepare an upgrade to release at the same time. However, I’d be willing to bet that the independent developer did not get an advance preview and is frantically trying to fix nuances/bugs. My advice – backup before you upgrade. There’s a good possibility that a plugin or theme will break WP3.5. And if at all possible, upgrade on a development instance before you do it on your production instance. That’s what I did and I’m glad that I did because I found issues.