I just started using the new Gmail gadget for Google Desktop. It's really nice, you can trash/reply/archive right from the gadget although it doesn't have any notification features such as sound or systray bubbles it's still easy to see what's new at a glance.
I usually have my personal mail open in an FF tab, the whole thing blinks annoyingly with an ok box when a new message comes in. Work mail goes to both BB and Outlook, on occasion my hip vibrates before outlook has refreshed, I glance down read who its from if its important I generally do a quick snap on F9 (outlook hot key to check in with server immediately). If not, I get a popup on my desktop anyhow.