Is that legal to replace the ads? I would think it is against the TOS of the site.
I absolutely hate plugins/companies that just routinely cover up other peoples advertising. It's not a smart move IMHO.
Makes even more sense to buy and kill a service hurting you.
We're not interested in cheating Google out of their ad revenue, although we suspect the Gmail ads aren't making that much revenue anyway.
Update: I should also add that we have a good relationship with Google, and we were a launch partner for their contextual gadgets platform: http://googleenterprise.blogspot.com/2010/05/putting-email-i...
If that were true, I'm pretty sure Google would have either 'fixed it' so that they do make revenue, or removed them.
Personally, I'd expect those ads on GMail certainly make a few million.