I doubt the major sites (party, stars, etc) are rigged. They have too much to lose if it gets leaked or figured out, and they make plenty of money with an honest game.
Some disagree, but those being vocal about it are usually fanatic and have little more than anecdotal evidence to back it up. They focus on things like “action flops” to get more money in the pot and therefore generate more rake, and predictive dealing to equalize the playing field a little so that bad players can stay around longer. I have yet to see anyone with real evidence of this.
On the other hand, there has been analysis showing random shuffles, though with a small sample size in this case:
http://groups-beta.google.com/group/rec.gambling.poker/browse_thread/thread/caa79fd079bee55d/3c3f29d3340e65d7#3c3f29d3340e65d7
Paradise poker has this to say about their shuffling algorithm:
http://www.paradisepoker.com/shuffling.html
And pokerstars mentions theirs here:
http://www.pokerstars.com/security.html
I suppose it’s possible that some of the smaller sites might resort to a rigged game, or the major sites might do it at the play money tables to get people to take the real money plunge, but it would take a lot of work to both rig the game profitably and make it hard to detect. Beating the play money tables is easy enough without rigging it, so I don’t see it being worth the time and risk.
I think you nailed it. Over the weekend I can think of at least one straight flush I would have made if I hadn’t folded my 45s preflop, and probably others I didn’t notice. Same with quads.
Playing online I get a chance to see a lot more hands than I would at any live game, so only the huge or unexpected hands get remembered. People are very good at recognizing patterns, and it’s natural to attribute a rush due to randomness as one due to design.