I'm having a rather bizarre DNS issue with Snow Leopard.
Certain sites - MSNBC.com being the most noticeable for me - have an odd issue with DNS, in all browsers. After not visiting the site after a while (30 minutes or so), the first attempt to access MSNBC.com results in a DNS error. Refreshing 1-5 times resolves the issue until the next ~30 minute period of inactivity.
Seen this on three separate Macs at this point. One from-the-factory Snow Leopard install, two upgrades. Most sites are just fine. I Google and found other reports of the same thing with MSNBC, but no solutions.