I have Vista Ultimate 64, Ubuntu 8.04 x64, Mac OSX 10.5.2 on my laptop and I used to have XP Home 32 on it as well. I have to say, Vista is great. I used to HATE it....no, I used to despise it to the point where I swore I'd never upgrade. However, when I went to get my college laptop, the new shiny HP dv9700t's only came with Vista, so I decided to go for the best one available and to my surprise, Vista had really improved. My first experience with Vista was horrible, programs crashed, UAC was a huge annoyance, hardware failed, drivers didn't work, and graphics were horrible. However, it's a lot better now, and it actually runs games BETTER THAN XP. I had a significant FPS increase in Vista over XP (most people say the other way is true, but for me, Vista won).
As for networking, it works fine with XP, Ubuntu, OSX, other Linux distros, even 2000/98/95. The only downside with Vista is that you can't share things in your C:/Users folder without sharing the entire folder. That means you can't share C:/Users/yourname/Desktop/shared_stuff without sharing C:/Users and all the contents inside of it. Annoying because I used to share folders out of my Desktop on XP all the time, but not a huge deal, as you can make folders anywhere outside of C:/Users and share normally (I made a C:/My Documents, like 95/98 had, and it shares just fine).