Updates through version 2.3 of Rybka are included with Rybka 2.1. All that's required is to send Convekta your registration code.
Also, Rybka works within a wide variety of engine interfaces, including Fritz, Chessbase, Arena, Chess Assistant, and almost any recently developed GUI. I have not tested it in recent versions of Chessmaster (with UCI support), but it should work there as well.
When chess engines are discussed, there is a tendency among reviewers to overdo the hyperbole. Part of this is natural enthusiasm, but one does get tired of watching one engine or another come out on top, depending on who runs the test, the conditions, opening books used, etc (no offense to engine testers intended). Occasionally there is some consensus that one engine is better than the others. This happened with some versions of Fritz, and with Shredder. However, the situation is now slightly different with Rybka. This engine, with it's very modest and unassuming name (roughly translated as "fish" in many Slavic languages) has done more than produce agreement among the majority - in the case of Rybka, almost everyone agrees that it's the strongest engine, bar none.
Furthermore, Rybka's rating is around 100 ELO over the next strongest engine. So this is not a matter of a small increase - this is a large jump in playing strength and it accounts for the wide agreement as to the engine's robustness. Indeed, one is hard pressed not to find a rating list in which Rybka holds the top spot (see below). ChessOK states that the ELO on this engine is over 3000. This is probably quite close to the mark.
The program's author, IM Vasik Rajlich, states that the reason for this leap in playing strength is Rybka's evaluation function, which is purported to be different in conception from any other chess engine. Of course, we'll never know for sure - and every engine programmer is certainly entitled to keeping a secret or two. Of course, it certainly doesn't hurt that Jeroen Noomen (of Rebel fame) designed the opening book for Rybka. Even so, without the benefit of this opening book, Rybka is still incredibly strong.
Convekta has really pulled it off with Rybka. It is without a doubt the strongest engine available today. And it's simply great that the engine is available in a UCI version, which ensures compatibility with every popular GUI out there (Arena, Chessbase, Fritz, Shredder, Chess Assistant, etc). If you do purchase the engine for use in Chess Assistant, make sure you read the engine setup notes below.
Engine setup notes:
Installation of this engine has to be done manually, and the documentation for doing this is located on the CD. It's not a difficult procedure but I think it would be nice for future versions to have a setup program. I also noted that the instructions made reference to setting the engine type to be "Rybka". However, in the version of Chess Assistant that I'm using (9.03 as of this writing), there is no Rybka engine type, so you should select DLL (UCI) as engine type in the engine's setup dialog box (but only if you're using the dll version). If you're using the executable version, then you need to set the engine type to "UCI".
Personality Settings for Optimal use with Chess Assistant (Tools->Engine's Setup->Personalities)
As can be seen in the above screenshot, Rybka has a number of interesting settings. There are a few that I'd like to call attention to. The first of these is the setting for limiting playing strength. Note that you must adjust both the playing strength slider (UCI_Elo) and check the "UCI_LimitStrength" box to use this feature. You also might want to adjust the time settings on the right hand side of the screen, especially if you find that Rybka is playing too quickly for you. Rybkachess.com has a good FAQ that discusses some of these settings.
I would also suggest checking the "Preserve Analysis" box. if you are planning to use Rybka for either the background analysis or interactive analysis functions within Chess Assistant. These functions make heavy use of hash tables and previously analyzed positions. Don't forget to uncheck "UCI_LimitStrength" if you're using Rybka for analysis.