I got my whoosh back. I lost my mail whoosh after updating to 10.7.2
I resolved it by going into mail preferences, general tab & changing the sounds to "none" and unchecking "play sounds for other mail actions".
Then I quit mail from the top menu bar. I restarted mail, went back into preferences did the opposite: changed sounds to "new messages sound" and checked "play sounds for other mail actions", I then quit mail again from the top menu and then reopened it. Magically, my whoosh was back.
I don't know why it went away after updating. And I don't know why this fixed it, but it did.