Working with e-mail for the best part of my 10-year career (my first "real" IT work was linked to e-mail and "groupware" implementations), and particularly working with a system with a fast and reliable index system (Lotus Notes) taught me to:
1. Never delete an e-mail (except jokes)
2. Never create folders and "waste" time organising e-mails
Number 1 is for obvious reasons. Nobody can claim to have or have not said something by e-mail. You KNOW what's been said.
Number 2 might be less obvious, but it resulted from experience: I used to organise my e-mails, and dedicate a good part of the day/week into keeping my inbox clean. And then, when weeks later I would need a specific e-mail, I would go to the "All Documents" view and search the whole mailbox, which "kind of" defeats the purpose of organising e-mails in the first place.
So I gave up organising my mailbox, and adopted a "search when you need it" approach.
A few years forward and here I am. No Lotus Notes on my machine - MS Outlook only. It looks WAY better than Notes. But it SUCKS big time. Search is absolutely crap and slow. Try searching for an e-mail for which you only know the sender's mail domain. Or better, search in all folders at the same time. Or (I love this one) try searching on moderately-sized (50MB) Local folders...
Sure, it can be done. But it's not easy. And slow. And not comparable to a Notes full-text search on a 500MB mailbox. And you have to know where the string you're searching for is located: Body or Subject or From or Send To, etc. What if you don't know? Chances are that if you knew all that about the message you're searching for you would probably know as well on which folder it was stored, right?
Consequently, it was quite funny to find out that Gmail's "revolutionary" way of working with e-mail is exactly the same way we - old Lotus Notes users - have always used our mail. Don't organise, search for it ;-)
Lotus (the company, not the software) may be dead, but it sure had guys with vision.