Everything I read said that the GNOME 3 PPA for Natty would be very experimental, cause sudden death, etc until April 28th. Well, today is April 28th, so if I start using GNOME 3 from the PPA will it work entirely correctly now?
I read (source) that GNOME 3 will break Unity in 11.04 and the issue won't be fixed until 11.10.
If you don't mind losing Unity, there probably is a way to get GNOME 3 working correctly but it definitively won't be painless (as there is no official support).
If you want to experience GNOME 3 now, I suggest you check out Fedora 15 (currently in beta).
The Desktop Team has been very busy getting Ubuntu 11.04 out the door. The transition to Gnome 3 is very big and there has not been sufficient time or attention put into the Gnome3 PPA so it is still experimental and not recommended for use.
In other words, installing the PPA and upgrading your system will definitely result in you having various issues even in Unity. The gsettings migration also causes many integration issues. I have previously lost work because of gnome-power-manager problems when the computer auto shut off because I was unaware that my laptop had become unplugged 2 hours previous.
Do not even attempt to use the PPA unless you are very familiar with how ppa-purge works.
For a smooth Gnome 3 experience on Ubuntu, wait 6 months for Ubuntu 11.10. The PPA may get better in the next few weeks but there are limits to what can be accomplished in a PPA.
It is possible to get Gnome3 working in Ubuntu 11.04(Unity, Ubuntu Classic and etc will not be available after install). Problem will arise when you will try to log in after the install. Not everybody is getting into trouble with it though, but some people do.
Another desktop environment should be installed like LXDE and then you should log in with installed desktop environment once, and then after that you can start using Gnome 3
Few articles that could be of a good use if you want to experiment
I tried to install Gnome3 on my own and broke system twice but in the end I got it working, only the problem was that my video card is not supported by Gnome3, so make sure you have right graphics also, I went back to Ubuntu classic by reinstalling system PPA-PURGE did not help when tried to downgrade to previous gnome version. Maybe with a bit more time there will be a solution, could not find it for now