Ive been using gmail for a long time and have been very happy. Coming from a blackberry I've been used to the push email so I set up a yahoo email address. Since then its been spotty to say the least. Sometimes it works ans sometimes it doesn't.
The thing I hate the most is when you send an email via yahoo they add spam junk at the bottom of the email which I hate.
So the solution that is working best for me is to forward my gmail and .mac addresses to my yahoo account that way I'm notified right away via the yahoo push. When I hit he mail button all my accounts show up and I can see my email. Then I respond via my gmail. It is an extra step nut its working for me until gmail gets on thebpush wagon.