The good. This is a plugin many people (me included) have been waiting for years. Most important, it allows you to have all your buddies in one place, and communicate with them in a stemless way (no matter whether they use GTalk, Yahoo!, AIM, ICQ, MSN, IRC, or whatever). This has always been one of the biggest advantages of using Gaim/Pidgin/Adium. But there was still one important protocol which it could not do, because the developers of this protocol tried their very best to make this impractical: Skype. Still, a while ago, in a sudden outbreak of common sense, the Skype developers released a public API, which now made this plugin possible.
The bad. The plugin requires Skype to be running as it uses the Skype public API to communicate with a running copy of Skype. This is needed since reverse-engineering the evil Skype protocol, while not impossible, would be a daunting task (see Silver Needle in the Skype for more details about this).
Many people are using Gaim/Pidgin/Adium because it is Free Software (GPL). It is also running in more or less the same way on any operating system. This is particularly interesting for people using proprietary instant messaging clients on non-Windows machines, because they had to stick with much older versions (while for Windows, Skype is at version 3.6, for Linux it is at 1.4 and for Mac at 2.6), this assuming there was some version for their operating system. These are problems that the current plugin can unfortunately not fix, since it relies on a running (proprietary and possible outdated) copy of Skype. Still, the plugin itself is GPL.
The uggly. No voice or video support, but this is a general problem with Gaim/Pidgin/Adium, which will only get solved if someone is willing to invest some time into it. The plugin itself worked fine for me so far with Adium, even though there are some Known Issues (see readme).
Related (good) news: GTalk now interoperates with AIM and ICQ.