I installed Google Talk last night, and it looks very cool. I just hope I can get my friends to use it. I installed Google Desktop a bit before that, and find it very useful, but I don't like that certain features of it are only available when it's docked on top of a giant portion of your screen, including your taskbar. Also, it doesn't "support," network drives for the indexing of picture files, but it works fine for any other kind of file. It will only let you determine whether it runs all the time when you first install it, and never gives you that choice again. The only way to make it only come on when you ask it, as far as I can see, is to change some registry settings, which is beyond most computer users.
In addition, it is always on top, but even when it's occupying a third of my screen, it still scrunches things into spaces where they don't fit, while it leaves tons of whitespace in the weather "panel," and others. It has myriad plugins available, including a reminder application, a calendar application, and others. It comes with a neat feature that indexes all of your gmail emails, and even alerts you of new ones and displays them, but when you display them in your browser, it doesn't give you the normal gmail user interface, with which you can archive messages, categorize them, report them as spam/phishing attempts. All it shows you is the bare message.
But, until they fix some of the functional problems I have seen, I won't use it. It's a shame, because I think it'd be a very useful program. I just hope they can make it less intrusive, and more configurable out of the box.