I'm a MBA Rev. A user (first day 1.8/SSD). I recently upgraded the stock SSD with a Photofast 128GB model for more space. Both before the SSD upgrade, and more noticeably after, my Windows XP virtual machine seemed to run poorly: frequent "pauses" and generally really slowly. At that time I was using Fusion; I decided to give Parallels a try. Slightly lower RAM footprint, but still slow. I found that disabling the shared folder feature helped somewhat; adding the NtfsDisableLastAccessUpdate registry key also helped somewhat. Still frustrated, I tried Fusion 3; that didn't help. Then Parallels 5 came out, and I had missed the free upgrade cutoff by 3 weeks. Even more frustrated, I decided to try VirtualBox. Oh, my. It installs easily. It does everything I need. It runs smoothly (no pauses, good speed in the VM). It's FREE. Bonuses: the RAM footprint is even smaller; the hard drive container file seems smaller (even with exactly the same contents inside the VM). The only downside is a lack of "coherence" or "unity" mode, which I never liked anyway. I am a rock-solid convert to VirtualBox, and highly recommend it over the commercial products for running a Windows XP virtual environment (I have not tried Windows 7, nor will I; with only 2GB of real RAM in an MBA I cannot imagine that will go over well).