Tip of the Day - Clearing Local Resolver Cache
In the name of performance Apple has in Tiger and Leopard decided that cacheing DNS lookups locally was a good idea. Normally it is, but when you are debugging DNS problems or changing DNS records it can be quite a pain if you forget about it. Well as long as you remember, its simple enough to clear the cache:
Tiger
lookupd -flushcache
Leopard
dscacheutil -flushcache