After reading the iOS5 upgrade on the Lifehacker website, I decided to upgrade my iPad2 to iOS5. It's unofficial, because iOS5 hasn't been released yet. The version mentioned on the Lifehacker websites is considered to be the Gold-Master version. Meaning that it's the final version, waiting to be released somewhere this month.
First I installed the iTunes beta version as mentioned and downloaded the appropriate iOS versions for my iPad and iPhone. The upgrade went extremely well. Just remember to backup your device before the 'upgrade' proceding.
After the iPad upgrade, I decided to upgrade my iPhone3gs. This went as smooth as the iPad upgrade.
The biggest new feature for me so far is the possibility to use custom text/notification tones. The iPhone3gs also feels more responsive.
There was one annoyance with the initial configuration of the iPad;
My Apple ID was a basic username, and not an e-mail address. This is NOT accepted by the initial iOS5 configuration wizard. Your Apple account NEEDS TO BE an e-mail address. It took me a while to set that up properly in my online account settings.