After you play with iOS 5 you can get back to last release:

If you do not want to keep iOS 5 on your phone.

To downgrade:
- Put the phone in DUI mode by plugging it into iTunes, holding the home and lock buttons for 10 seconds then releasing the lock button but not the home button. iTunes will say it's detected an iPhone in recovery mode.
- Option-click the "Restore" button, and select the 4.3.3 ipsw file, which you may need to download from here:

Download iOS 4.3.3 / 4.2.8 Direct Download (Official from Apple)

• iPhone 4 (GSM)
• iPhone 4, iOS 4.2.8 (Verizon)
• iPhone 3GS
• iPad 2 WiFi
• iPad 2 GSM
• iPad 2 CDMA
• iPad
• iPod touch 3G
• iPod touch 4G

- Restore from your backup and you're sorted.

This is potentially dangerous, but your phone will never be 'bricked' by an Apple released update, even if it is beta. Not unless there's a massive bug, which is always possible, but highly unlikely