Unless you are living behind the moon you've most likely noticed that Google today unveiled its own instant messaging thing.
Technically this is absolutely no big deal: The service is based on the the Jabber protocol family, which isn't much more than a fancy name for a bunch of RFCs describing data exchange via XML. In the past people have been running Jabber servers (pretty much like what's behind talk.google.com) as long as the project exists, and there are quite a few server implementations available — commercial and non-commercial.
The software issues aside, Google needs a bunch (resp. a bigger bunch because we are in Google land) of servers for the Jabber daemon to run. Servers? Exactly, that's the sort of computers which Google owns a gazillion of. So no big deal either. What's left is the problem of building up a solid user base. With regard to this they luckily had a few thousand (most likely more, I don't know) already in their databases: Every GMail user can automagically log in to the IM service. No sign-up required and the user base is just there.
So even if Google doesn't earn a single buck with the whole project, they won't enter a loss: They not only have provided yet another reason for people to sign up for GMail, but they also are on par with Yahoo! and MSN and probably also AOL in the instant messaging world. And all this for a reasonably low price, compared to what they had to invest into the search infrastructure.