I made the mistake of upgrading from Fusion 1.1.3 on my MacBook Pro to 2. First, while I'm ranting, let me just say that VMWare's upgrade process for Fusion is something right out of 1992. But let's say you do go ahead and upgrade. Here's what you're in for.
I use Fusion to build Firefox on Windows and sometimes Linux, and yesterday, after upgrading, I tried building in both my Windows VMs (I have an XP and a Vista). The Fusion program itself really dragged my whole system down. I couldn't flip between spaces, my apps wouldn't respond to the keyboard or mouse--it was brutal. Eventually--literally minutes--I got the first VM booted, and did my build: 159 minutes! I tried the other VM and it took forever to even boot. After some more testing, I went to see if others were having trouble. Turns out I'm not alone.
So I decided to try and re-install 1.1.3. That went pretty well. It complained about a newer version of the software (notice the use of the word "newer" and not "better") being installed, but it let me do it. When I was done I tried booting my machines. The Vista VM, which had been shut down was totally broken, with an error about the config file (.vmx) being corrupt and having features for a newer version that were incompatible. I then tried the XP VM and it booted (it had only been suspended).
I took a peek at the two .vmx config files to see what was different, and after making the following change, the Vista VM booted fine:
from: virtualHW.version = "7"
to: virtualHW.version = "6"
I can't believe how much better things are now. Even with 4G of RAM on this machine it thrashed until it was totally unsable with 2, and runs really fast under 1.1.3. My advice is that you don't upgrade to 2.* until you read something about performance and better i/o in future release notes.
UPDATE: Taras says it's working fine for him, but bz reported similar issues to me. I'm sticking with 1.1.3.