I have 2 main email accounts, and realized yesterday that I had about 15,000 emails between them! Argh!!
A great majority were sales/newsletter/special offer type emails that I would skim (or not), but not bother to delete in a very long time. I have to say that I like gmail even more these days (my main emails are with yahoo and gmail.) It was much easier to do a search in gmail and delete 100's of emails at a time. I also like being able to apply labels to incoming and existing mail. It makes for an extremely easy filing system -- and also an even easier way to find hundreds of emails to delete!
After about an hour of concerted searching, deleting and un-subscribing from newsletters, I'm down to about 3,000 emails. Another hour or so and I should only have those that deserve saving (emails from family, friends and the occasional business offer.) It feels great!