iOS betas, especially first builds, are usually pretty buggy. Considering this isn't due for a consumer release until this FALL, it makes sense that there are still many kinks to iron out.
I've run in to a few things.
* Collections on my desktop will have a "badge" notification but none of the apps inside of the collection have unread notifications.
* Safari has force closed a few times randomly while trying to paste text or do bookmark management.
* Photo Gallery force closes when opening a picture sometimes.
* When I'm editing a photo in the photo gallery, and go to adjust something like red eye or brightness, there is no option to save or go back. I have to press the home button to go back to desktop. Weird.
* There's nothing in the status bar that tells me I have pending/unread notifications. from the keynote, I thought there would be an actual icon that summarized my notifications (
http://bit.ly/mPi30E) but I guess this was just a design element created for the keynote and doesn't actually exist.
* Newsstand doesn't seem to let you purchase anything yet. I guess the market doesn't exist yet.
* App compatibility with iOS5 has been really good so far. I haven't had much experience with iPhone or iOS apps "not working" with iOS5, except for Netflix, which wont allow me to search for anything (I can't focus the search textbox).
That's about it for me. Just quirks. They'll get ironed out, I'm sure. Actually there's built-in bug sending to Apple that happens if you opt in to it upon starting iOS5 for the first time. So the Apple developers, I'm sure, are capturing all of these random glitches and quirks as they happen.