Vista is supposed to use ALL the memory. That is called pre-fetching which all modern operating systems use. I have a system with 12GB of RAM and Vista uses ALL of it. Pre-fetching uses up all memory for commonly used programs. It will release memory as needed.
I've used Vista 64 bit since it came out and I have nothing but good things to say about it. Sure there are things that annoy me about Vista, but there are things that annoy me about every OS. Windows 7 has it's own annoyances.
People talk about all these bugs that Vista has, but tell us what bugs? Don't read on the internet about how people hate Vista, use it for yourself and tell us why you don't like it. If your system blows, then don't complain. Vista was probably not made for it.