Gmail has IMAP. Google Docs has an export feature. Google Reader lets me export my subscriptions.
It'd be nice if they had a one click export that'd send you a tar with all your data ever, in every reasonable format, but that's not as easy as it sounds ;)
Is there a standard format for storing email? I would like to archive all my mail using Gmail's IMAP feature, but what happens when I want to find something in 30 years? For example, I'd think that an Outlook data file would not be a good choice.
mbox and Maildir have both been around for years, and will be around for years to come. Both are easily converted into each other, and there are many common tools for reading and writing them. Most major languages have APIs for working with either spool type.
mbox has been around for at least 20 years. I don't know if it will be around for 30 years, but it's such a simple format, that I'm sure you could deal with it in 30 years even if no tools still commonly use it--you can open it in a text editor and make sense out of it without any parsing, at all, for example. (MIME encoded messages are much harder to parse, and can contain infinite other formats, but the actual email is always gonna be easy to get at.)
I used to use Linux mailspools, or whatever, but I really don't know nowadays what's cool. I just use both the Vista email client and Gmail. When one of them fails, I'll just upgrade/try another one.
It'd be nice if they had a one click export that'd send you a tar with all your data ever, in every reasonable format, but that's not as easy as it sounds ;)