Alternatives to Google Notifier
Just installed Mail Notifr - $2.99 on AppStore, or free if you download the previous version here: http://ashchan.com/projects/gmail-notifr

At least the paid version looks nice, clean, and in terms of functionality it's pretty similar to Google's Notifier, less Calendar notifications. Mail check frequency can be set in Preferences (Google's was a hidden undocumented feature); multiple GMail accounts are supported. I just hope it's stable and reliable enough. We'll see.

Update: so far so good. One little nice thing about this app is that when the system wakes up from sleep it checks for email immediately, whereas with Google Notifier you had to wait another 5 minutes or force mail check manually.

Update 2: one other thing missing compared to Google Notifier is handling of mailto: links and in general, redirecting to GMail when trying to send mail from any desktop app. Mail Notifr doesn't do this. Would be nice to have actually.