I just downloaded the update, it told me something failed and I need to restore my iPhone. I am on try 3 and it is still failing every time it tries to restore. It's giving me error code 1013. I would stay away from this update for at least a day or two until others give feedback. It doesn't seem to be that critical of an update anyways.
Warning Note: This will result in your iPhone 4 baseband being upgraded to the latest version.
How to Fix Error Code 1013:
Mac OS X:
Step 1. On your Mac, go to your Applications folder.
Step 2. Now navigate to the Utilities folder.
Step 3. Launch "Terminal".
Step 4. Type "sudo nano /etc/hosts" (without quotes) and hit return.
Step 5. Enter your password
Step 6. Use the down arrow key to find the gs.apple.com entries. Once the cursor is in front, make sure you comment out the line(s) by entering # in front of the text.
Step 7. Save the file by pressing CONTROL+O.
Step 8. Exit the nano editor by pressing CONTROL+X.
Step 9. Restore your iDevice.
Windows:
Step 1. Start > Programs > Accessories
Step 2. Run Notepad or WordPad
Step 3. Click Open.. from File menu.
Step 4. Browse to Windows/System32/drivers/etc
Step 5. In "files of type:" select all documents
Step 6. Open "hosts"
Step 7. Delete all line that has "gs.apple.com" or something like that
Step 8. Hit Save
Step 9. Restore your device