Many thanks for the info guys. My board has just hit the 130GB/mth bandwidth barrier so it looks like I'll be forced to get a dedicated server soon. It's basically a toss-up between Rackshack and Servermatrix, depending on who privides the best price/specs. I'll definitely go for a Linux server though, no doubt about it.
Quick question for those of you running boards on dedicated servers: what kind of CPU does your server have? I'm currently looking at a P4 2.2 (with 1GB RAM) and am wondering whether it'll be enough...