Alright, Im thinkin about buyin Vista, but, First, I wanna know what problems their are, as of the most resent update.
If you thinking about upgrading your existing machine, I'd strongly recommend you download Microsoft's Vista readyness tools -- it will check out all your hardware components, and tell you whether or not there are any known compatibility issues. (e.g. your webcam / printer / scanner / soundcard / networkcard / videocard / all of the above may not be compatible with Vista. always nice to know up front whether you'll be able to use them after the upgrade.
Secondly, make sure that you know which version to get. there's a lot of different flavors of vista, most notably both the 32-bit and 64-bit editions. both have good and bad things: the 64-bit edition can access >4GB of RAM, but there's quite a few programs that are not compatible and refuse to run on it. Especially important when it comes to device drivers, since you need to make sure that there are Vista x64 drivers available for all your hardware components, and many older hardware doesn't have these.
The 32-bit version of Vista has less compatibility problems, but you can't use more than 3.25 GB or so of RAM (the exact amount depends on your motherboard)