OK, I've only used Proteus for a couple of days, but I've already found enough annoying bugs to start complaining about. For a program that's up to version 4, and that costs $15 (compared to other **free** multi protocol chat clients) this thing has too many bugs. Some highlights: the status message doesn't 'stick'. I have it set to show my icon in my contact list, and use the (*very* cool, BTW) feature to show the currently playing iTunes song as the status message. But it has this weird habit of disappearing. I don't know if it disappears for people on the other end, too. And the prefs don't seem to take effect right away, sometimes. One time I had the "connecting" sound enabled (biiiig mistake!) and one of the services was taking a long time to connect. the sound kept playing and playing and playing, so I went into prefs to turn it off, but it didn't work. Had to quit the program and start again.
Also, now for some strange reason, pressing cmd-H doesn't hide Proteus (yes, there are other programs visible to switch to), and clicking on a contact in my contact list doesn't select them, so I can't get info about them. Actually, now I can't do anything with the contact window, close it, change status, anything. Looks like I have to restart the program. That fixed it, but the the problem is that kind of thing happens waaaay too often.
This program has some really cool features that Adium doesn't have, like invisible mode, and the itunes thing, but overall it's B.U.G.G.Y., too buggy for a prog that's supposedly hit version 4 (not to mention the $).