Maybe consider using SpamSieve. You can turn off mail sounds and have the spam program alert you only when you have real mail. Plus it is just a great spam program vs Apple's Junkmail system.
After booting up lion and setting up my mail accounts, I heard a sound that I haven't heard in many many many years. I was literally taken aback when my mac made that sound for the first time in so long, but I am definitely glad it's back.