Of course I am trying out Google Talk, at least long enough to figure out how to make most of it work inside of Trillian. Feel free to find me online if you want to play with it, but I'll tell you upfront that it's rather bland and feature-sparse as IM goes. At least it's very 'clean' and 'simple.'
If you're going to dominate the world, at least the world of software, then an IM client is pretty much obligatory. They're also really, really easy to implement -- it seems that whenever I have to come up with a software design/prototype for something, IM ends up listed as an ancillary feature. In Google's case, they didn't have to implement as much as they based theirs on pre-existing Jabber software. They did add voice chat to the mix, which is nice, but also not groundbreaking.
In order for it to be groundbreaking, I would have expected something more... Googley... i.e. I would have expected them to allow you to save your IM conversations on their servers and search them later on, or to be able to lookup terms/acronyms/names that other people use (Trillian does auto-Wikipedia transclusions), or I would have expected some sort of interesting 'conversation' integration with GMail given that the Talk client is already leveraging your GMail contacts. One of the things I've noticed about GMail is that the conversation UI means that when you are e-mailing with other GMailers, it can frequently start to approach the brevity and speed of IM -- a seemless transition between the two environments would be a difficult but useful innovation.