I consider myself a pretty heavy email user, I switched to gmail at the very beginning and haven't looked back. I was using it to check my uni email [when I had it], my ISP mail [when I had it] and I have 2 gmail accounts going into one.
I hardly get any spam and don't miss anything that you get with third-party POP3/IMAP clients. In fact, I would never use the download+delete-from-server mode of POP3 again since you can't see your mails when travelling without your main machine - this way I have a single point of access to all my emails, I can get onto it from anywhere in the world with internet, have it pushed to my iPhone via gmail push (along with all my contacts/calendar items that are continuously synced too) and have the ability to search through it pretty quickly thanks to gmail search.
I use my email as a notebook, todo list and keeping track of pretty much everything. Not sure what I would do without it. I take exceptional care when accessing it outside of my trusted network and change the password every 3 months or so.
I've also scanned in all my bills+other household bits and bobs as PDF files and stored them on my Google Docs... If my password is hacked, I'm done!