I believe this doesn't work if you want to use Gmail's offline feature. Also, the maximum seems 3 accounts?

Here's the official explanation (with this exact use case): http://gmailblog.blogspot.com/2010/08/access-two-gmail-accou...

Interesting. I don't use the offline feature, so it had never come up as a problem here.

Wow. The multiple tabs + account switcher thing works surprisingly well.

Have you ever run into problems using it this way? Seems like this is somewhat outside of the normal usage (maybe because of all of the disclaimers when you add extra accounts?).

So far, no. I've been doing this for about a week, and - as far as I can tell - it works fine. I don't know if this is actually a supported thing, or something that only works by happenstance, or what. But for the time being it seems to work. <shrug />

You can do that? Do you have to switch back and forth every time, or can you keep multiple accounts open at the same time?

Nah, it works fine... each account stays open in it's tab and I can just switch tabs to see each account I care about. Note that I've only ever tried this using Chrome, so I don't know if they do something special to make it work or not.

should be noted: Logging in is a pain. Cookie and FF default auth details are saved using the same underlying mail.google.com domain, it doesn't bind the correct saved authentication detail with the correct account. CNAMES have no effect on this.