In the beginning, there was nothing -- which exploded - Terry Pratchett
The "GMail Program Policies" document, available here now lists under the section titled "Prohibited Actions", the following, among others:
Google can probably kill the GMail eBay sales overnight simply by requesting auctions sites like eBay to remove all such listings. But private transactions between two people are probably outside the reach of Google's long arm. It's all a matter of (low) supply and (high) demand.
In the case of reverse engineering, this is where things get interesting, because then we could suspect the developers of all the pop3-to-Gmail programs could be in breach, if they had to reverse engineer the GMail login process. That would include programs like PGTGPM and eMail2Pop.
And about the third restriction. One of our readers mailed us suggesting that peer-to-peer file sharing based on GMail storage was in his opinion an upcoming "Gmail hack". The folks at GMail must have read our reader's mind.
There are many more restrictions listed on Google's document. So, now that sales are prohibited, ideas about possible uses for three spare gmail accounts ipohype@gmail.com, mediahype@gmail.com and NiceTryYahoo@gmail.com, are welcome. µ
See Also
Google's Gmail: POP3, online backup, money making machine