Today the UK's MarketingMonitor newsletter published a really great Case Study on a viral marketing campaign that a UK-based interactive agency used over the holidays to get attention and new clients. If you're remotely interested in viral marketing (and who isn't?) then definitely
and scroll to the Case Study.
(BTW: A "cracker" is not a salty snack in the UK. It's a brightly wrapped tube with a little gift inside. You pull at the ends, it makes a cracking noise and the gift pops out.)