ubuntu is a good os but like everything out there isn't perfect and doesn't support every peice of hardware.
windows 7 is probably the most complete OS to ever grace us in terms of compatability. I've had very few occasions where it didn't find a driver and get it working.
The adapter i mentioned isn't out yet as far as i know. What to do is don't take any shortcuts as you may just end up disapointed and out of pocket.
There are a few graphics cards out there that can support more than 3 monitors. It's not about the number of monitors that makes eyefinity special it's how it does it.
so lets assume you don't have any display port monitors and just have 3 monitors with dvi. Connect 1 or 2 with dvi and one must come from the display port using an active display port -> dvi adapter
2 x dvi 1 x display port
1 x dvi 1 x hdmi 1 x display port AMD Eyefinity Validated Dongles
this link shows approved adapters you can get that will work, worth checking.
obviously having display port monitors helps a lot here but not essential. ATI Eyfinity review
A link to a review of eyefinity, This review also shows the pro's and cons of using it though probably a little out of date now on some of the info but page 2 shows the potential setups you can go with.
eyefinity is amazing there is no question of it and support in games will get better over time, set it up the right way from the start and enjoy.