How many Google accounts do you have? One or two personal Gmail accounts? A Google Apps account for work? Or two? Then, of course, your wife/kids/partner/dog want to check their Gmail on your computer. To a limited extent, Google already allows multiple logins in a single browser instance with this sort of dialog:
However, this only works if with a Gmail account running alongside one or two Google Apps accounts.
Now Google is slowly rolling out a multiple sign-on service that makes switching between more than one Gmail account quite a bit easier. As CNet's Josh Lowensohn reports,
The new system, which was available on only 1 of 13 tested CNET employee Google accounts, requires opting in from a user's Google account management page. Once enabled, it provides quick account switching in Gmail, Calendar, Reader, Code, and Google's Sites products through the use of a drop-down menu that sits in the top right-hand corner of compatible Google sites...Two notable Google services that don't yet work with the feature are Google Docs and...Wave. Users trying out the feature also have to give up the offline features in Gmail and Calendar.
It hasn't appeared on my account yet, but here's a shot from the CNet report.
So is this feature a big deal? It's certainly handy and it points to the ubiquity of Gmail and the tendency for users to access Google's mail properties in a variety of contexts. However, as Lowensohn pointed out, this fast-switching mechanism between accounts has some significant limitations. Handy, a good idea, and not a feature found elsewhere, but not a reason to start using Gmail if you're more of a Windows Live Mail sort of person.
I do, however, have a theory about the bigger picture here. A quick read of both the Google Operating Systems blog (not official from Google; this blog is independent) and Google's Help Center post on the multiple sign-on feature suggests that this may be more about federation and single-sign-on to various web services than anything else. After all, Google Apps supports SSO and multiple third-party Apps in the Apps Marketplace enhance these capabilities.
If signing into your Gmail account suddenly had you signed in to Facebook, other Google properties (like Google Apps), your online banking, and your companies intranet, then that starts to become a reason to switch to Gmail. It's also a way that Google's rumored Me social networking platform could seriously differentiate itself from Facebook.
What do you think? This doesn't feel like a Google Labs feature that has just gotten a bit more attention than it deserves. It feels more like a harbinger of interesting things to come as Google expands its (currently) somewhat limited reach into the social web.
Note - updated at 12:58am, 4 August 2010, to reflect clarifications in the original CNet story.