Ours is pretty tight, but it appears to be wrapped in HTML over port 80 so it's getting through fine. Unless you have specific content blocking to source IP, which is pretty hard as it appears to use P2P - then it should work OK. It's endorsed by The BBC and it's for a good cause. The bandwidth shouldn't be an issue as it's batched so it only links up to send your calcultations and download new ones to process - about the same as a few ICMP Pings. I haven't had to make any modifications to my ISA ruleset and the logs appear to show http traffic over port 80 for new jobs to be done.
I don't wear green tights or carry banners, just figured I'd use my resources while I wasn't using them. A bit like eBay was originaly intended I think
[Edited on 25-5-2006 by desmobob]