Upgrade to MovableType 3.x

I think I'm going to upgrade my site (starting tomorrow or Friday). So if there are any technical problems with comments or searching that's why. It might even cause some viewing problems but those will be temporary since I can at a minimum push the pages (or at least the main page) back on-line.

I'm not worried about the upgrade in general, I'm more worried about some of the plug-ins that I use might not work anymore and that will cause problems with rebuilds.

Does anyone know if I can downgrade back down to 2.661 if it doesn't work okay? My one big fear is my provider (1and1) doesn't let scripts run for more than 12 seconds and I'm getting pretty close to that currently and if this runs slower it could be a problem. I think it's only because I've got so many posts in my archives ( I think that's where it's choking). Other than that I love 1and1, very configurable and the prices are good.