First off, it happens waaaay too much. There's something odd about PWO's accuracy with everything obviously (Sleep Powder misses less than aqua tail, Crits happen a lot more than 5%, and I've missed 100% accuracy moves several times) and I'd like to see it state there was a critical hit when there is so we can test just how many times it happens out of 100 times. If it was consistently higher than 5% then we'd know exactly how off it was.
It really incorporates more luck in battling and that's extremely off putting for people like HOF and I who have worked hard to become great battlers. I feel like it turns the tables far too often and honestly mostly gives the advantage to the newer players. I can't imagine the great battlers have a need for crits to assist them in battle nearly as often as lower tier battlers, so when these great battlers do get crits it's largely unnecessary since they're already winning. Putting it bluntly I'd bet there's a strong relation between the quality of battler and the opinion on crits.
As for the comments such as nemo's I don't think we should be looking at it as "may the luck spin your way" because it should be about one's skill, strategy, and the quality of ones pokemon. Quite frankly, if it is causing great frustration among players then I don't see why we should just "live with it". Battling is more like a lottery now than it was before. By the way, crits don't really deter boosters as wiping out a whole team is worth the risk of taking too much damage... you'll hardly see an arcanine killing a dragonite because of a crit, or a metagross killing a scizor. It's annoying, often taking the fun out of battles. One of my good friends JD quit battling the other day and I'm sure crits were a small part of the decision...