I tried it and uninstalled it the next day. It has a nice potential but limitations are too severe. First of all, I am speaking of a Symbian version, your experience with other OS's may vary. Here are couple of quirks I could not get over:
1. Inability to collect mail from multiple Yahoo accounts. Heck, there is not even an option to sign out/in once you passed the initial set up. I have two Y! accounts that I use regularly and would like to be able to switch between the two. Symbian version does not have that ability for some reason.
2. There is no option to get rid of tabs/channels. All I want is mail/weather/search. I don't need all other crap (stocks, news, scores, etc...) but there is no option to turn off those tabs.
Again, this was on the Symbian version of the software only. If you want something close to a true push mail for free/very cheap take a look at the mail2web service.