Um, it's a neat idea, but what's the difference between running a Widget as a background process and just letting your email client (Eudora, Mail, Thunderbird, whoever) simply check mail every 5 minutes or so and notify you that you have new mail? It's not like GMail won't let you use POP3...
Sorry to be a bit of a downer, I just can't find the use for Widgets in general: i.e. if I want to know something in Wikipedia, I go to the Web site and look it up; if I want to use a calculator, I use the calculator app; if I want to know where my FedEx package is, I go to the Web site and look it up; and do I really need to know where the sunlit Earth is at any given moment? I know they're supposed to save time and all, but does 20 more seconds per operation really add up? The only Widget I'm running is the SyStat, which I find more compatible with OS X than MenuMeters.
Ho-hum. A GMail Widget is cool, I suppose... But the part I like best is QE2 - if I could only get Eudora to look like that in my toolbar...