I have purchased an Ultimate Edition for two PC's ... and a Home Premium for my laptop. I have encountered no differences between the two ... well ... other than the fact that Ultimate has a few useless extras and comes with a 32Bit install DVD and a 64bit install DVD in the same box. But other than that ... I don't think anyone in a small business will ever get any use out of anything Ultimate offers over Home Premium.
I'm lucky because I paid £17.50 per box for my Ultimate Editions.
Fully legal of course ... I just know the right people! yay!