It was really, REALLY annoying, but you just gotta try and get through these things. Though the situation is naturally stressful (as your business contacts may be receiving highly suspicious emails), you have to keep as cool as possible.
All I can suggest is to regularly update your passwords (just for your peace of mind) and the most important thing is to have a 'secondary' email. For this, I would say Google (Gmail) are best, in my opinion. They got back to me really quickly and were able to boot the hacker out of my account.
The main reason I like having two (or more) accounts is that it allows you backup if this sort of thing happens. You have your business contacts located predominantly in one email, and then things like Facebook, Myspace, eBay etc. in the other one (Gmail or your choice). It also means you have another email so that staff at Google, social networking sites and your bank (maybe?) can contact you.
As I said, it was extremely stressful and I lost a lot of sleep and work hours. I am grateful though, that nothing worse happened. Saying that, I know what sort of present I would have for the hacker if I ever met him. Here's a photo of me with a sampling drill from when I was doing some farm work.
Ahh, I'm not really a violent, vengeful person. I actually feel sorry for these people, because they are sick. I spoke to the bloke on chat - I know. Desperate and ignorant, is what they are.
PLEASE - look after all your data etc. - I hope this never happens to any of you! If anyone has any further suggestions for security in this regard, please add them here or write to me.