Many times.
They can help you, sure. As long as it's a legit beta then it's Apple's program and they can support you pretty easily. They may or may not ask to revert; but here's how the script usually goes:
1. Ask you about the problem
2. They will try / ask you to repro
3. They will run diagnostics
4. They will ask if you have a backup on iCloud
^ This is the important step. Have your stuff backed up because you need to be ready for the possibility you will be leaving with a wiped phone or will be hanging around the store waiting to redownload the basics over wifi.
5. If diagnostics shows a hardware problem, then the appointment pretty much stops there. They'll give you some options - depending on if you have an active warranty/Applecare or not - and you can decide what, if anything to do.
Most stores now do in-store repairs so if they need to replace the screen they will actually set up a time for you to come back (I heard some stores offer loaners in the meantime, but I haven't seen it happen personally?) If it's sufficiently bad they will tombstone it and give you a refurb on the spot. Apple refurbs are awesome so basically you're getting a new phone. (They used to do this a lot more quickly until they did in-store repair)
6. Everyone asks, but you will never get a phone except for the same config as the one you brought in. Even if it's the iPhone 4. They will give trade in credit for phones if you want to move up, but the value is very, very low.
7. If diagnostics don't show an obvious problem, they are going to ask to wipe your phone to latest public iOS. They have macs there to help with the process if need be. This is a very popular step because a lot of weird software problems go away with a wipe. Sometimes they need to do this just to decide whether the phone needs a fix or a replacement.
(Their mobile app ran really well but I'm a whiner and hate watching stuff on my phone)
