I bought a pro key and I've been playing with Aquamail, and I'm quite impressed by it. But there is one feature that I am quite sorely missing, and that is some sort of gpg implementation. There's an app already called APG which K9 Mail uses and would probably work just fine for Aquamail as well. I have to stick to K9 until some sort of solution is added, but I look forward to the day that it's there and I hope that it is soon.