Yes Tim,
I know what you mean!But alot of us did not really know the extent of the bugs prior to buying.There was supposed to be a total bug fix by this past summer,but it did not occur!Anyone that purchases Ryb4 are supposed to get a free bug fix online or sent the bug fix disc when it comes out.
Interesting enough,however,Ryb4 is still the strongest chess software you can commercially buy on the web....even with some bugs!Others,like Stockfish come close,but are still not as powerful.Talk has it that soon Stockfish and perhaps others will surpass Ryb4 in strength,but that hasen't occurred yet.Again,if you are careful in the endgame,switching engines to Ryb 3 or perhaps stockfish(if you have it)will insure a top notch endgame without worry about some hidden bug!See,Ryb 4's opening book combined with mid game play from Ryb4 is where it best strength is at.So switching to another top notch engine in the endgame will not usually make much difference...atleast in my observations.As to analysis mode,yes some problems,but that should be fixed in a few months...I hope!In the meantime simply do not use analysis mode or try the single line analysis if need be.I personally do not see a big difference between giving Ryb4 a very long time control to compute a move as compared to an infinite control which has bugs.If you have a slow computer,well alot of the Ryb software will not perform as good as it could anyway.

I've used all the Rybka's from 2.3.2a,Ryb3 for multiprocessors and now i'm using Rybka 4 for multiprocessors.There are a few bugs for sure.One of the main bugs is Bishop/Pawn endings where Ryb4 many times plays very weak.This can be verfied by searching the Ryb forums as well.I do not use "analysis mode"in my corresp games,especially with the other analysis bug present in Ryb 4 with freezeups.With a quadcore and Deep Rybka 4,there is no need to let the computer run for hours on end analyzing specific moves.
What I do is set the time control in 3 stages....6 hours...first time control(40 moves),3 hours,second time control(next 20 moves) and 1 hour for the rest of the game.I just "add" more time if necessary to my"side" after receiving my opponents move.This is more than enough time for Ryb4 to play its best,especially at 2000 MB!
But heres the key to the analysis bug in Ryb 4:
Don't use Rybka4 when there are just a few pieces left on the board like the Bishop/pawn.Simply switch the engine to Ryb3!!!That way,any bugs will be bypassed with the other engine from that position.From the hundreds of games I played with both Ryb3 and Ryb4 on multiprocessor versions,I do not see any real advantage or worry that Ryb 4 will outdo Ryb 3 with a minimal amount of pieces on the board.It was reported to me that some Rook endings have a kind of bug in the Ryb4 engine too,playing weaker than Ryb3 in the same position!So,I believe that if you use Ryb4 for most of the game and switch to Ryb3 in a few cases like i mentioned above,you should be ok!
I hope the bug fix will come soon for Ryb4,however!

Multiple Principle Variations.  See this discussion on the rybka board:

http://rybkaforum.net/cgi-bin/rybkaforum/topic_show.pl?tid=17586

Jupp53 wrote on 06/30/10 at 17:38:07:

Be warned - there's a bug in the engine where it will freeze if you let it sit for too long in a multi-pv analysis mode.  Vas has already promised a bugfix is forthcoming, but given his track record (Rybka 3+, anyone?) he will understand if we are a little skeptical.

Has anyone bought Rybka 4 yet? If so, is it much stronger than 3 and worth buying?