The only disadvantage I can think of is that you are running Vista. 🙂
Seriously, there is only 1 that I can think of. Let's say you have 2 identical laptops (in terms of hardware)
A MacBook Pro (2.2GHz Core 2 Duo, 2GB RAM, 120GB HDD, 128MB 8600M GT)
A Dell Latitude (2.2GHz Core 2 Duo, 2GB RAM, 120GB HDD, 128MB 8600M GT)
In terms of how Vista will run, they will be identical so long as the install is identical (they both install Vista Ultimate, they both have the same updates)
However, the MacBook Pro will not be able to tap-click (meaning you cannot just tap the trackpad, you will have to press the button) which pretty much every other laptop under the sun can do in Windows.
I am 99% positive that Apple has perfect drivers for XP/Vista sitting around, they are just waiting for Leopard to go Gold before pushing them out. So for now, the Dell can tap-click, the MBP cannot.
And that is the only disadvantage