I've not heard anything specific to STS. If my memory is right normal
server-based systems are five years which would mean mid 2006 or so. But I'm
not sure if that 5 years is a) right b) applies to products that came out
before they made this change. I.e. I don't know. (!)

They are still at the moment providing KB articles and fixes so it's not out
of support  yet at least.

The question of course is why you need support in the far-off future. I
still have an old STS-based site but they have just ordered a new WSS-based
site to replace it and although they will keep for the moment the old info
accessible on the STS based site, it wouldn't be that difficult to move it.

The STS site that is in question is the center piece of an custom ASP.NET
application and its just not going to be that easy to convert over because of
how all the custom code interacts with it (database structure).

We have 100s of other plain STS sites and we are currently in the process of
converting them all over to WSS and this has been very simple so far.

SharePoint Team Services 1.0 follows the microsoft  Office XP product
lifecycle, where mainstream support  lasts through June 30, 2006, and
extended support lasts through June 30, 2011. See
http://support.microsoft.com/gp/lifeofficefam" target="_blank" rel="nofollow">http://support.microsoft.com/gp/lifeofficefam and
http://support.microsoft.com/gp/lifeoffice for more details.