Remember Webb Simpson? He was the one penalized in May when his ball moved while addressing it on the green. This resulted in a 1 stroke penalty and, ultimately, Bubba Watson ended up winning in a playoff. The USGA appears to agree with Webb that this is a bad rule (see the linked article, O'Toole even states that a change in this rule could come as early as the 2012 revision). Personally, I disagree that even this rule should be changed. Changing the rule creates a grey area. Did the ball move because of the conditions or because of the manner that the player addressed the ball? When playing in conditions like that, when greens are fast and hard, players should adapt and "address" the ball accordingly (don't ground your club and you haven't officially "addressed" the ball, problem solved). Take, for example, the 1950 US Open. Hogan managed to avoid a penalty under this exact rule by adapting his game to the conditions. Personally, I do not believe that this is a rule that needs to be, or should be, changed.
Or, how about another blunder, the 2010 PGA Championship? Should we allow one to ground their club in a hazard? Obviously not. Grounding one's club in a hazard is an obvious means to test the conditions. Had Dustin Johnson actually read the local rules sheet before the tournament started, I bet that this would have been a non-issue. He would have likely error-ed on the side of caution and not grounded that club. Not being able to ground your club in a hazard is a good rule and it should remain intact. In fact, here's some unpopular opinion I'm sure, I'd take it one step further and do away with rakes and favorable bunker conditions altogether. Hitting your ball into a "sand trap" is no longer much of a penalty. In some cases, your odds of getting up and down out of a modern bunker are better than your odds of getting up and down from thick green side rough. Henry Fownes was on to something with his furrowed bunker rakes at Oakmont. Too bad that it didn't stick.
Maybe eliminate a penalty that a lot of weekend golfers HATE; stroke and distance? This comes up primarily with balls out of bounds and lost balls. Most weekend guys that I know will instead drop a ball in the vicinity of their lost ball or roughly where their first went out of bounds. Some will take a 2-stroke penalty (thus hitting 4 if it was their tee ball that was lost), others take only a 1-stroke penalty stating that it shouldn't be any worse than hitting a ball in the water. Others won't take a penalty at all, after all losing a ball was penalty enough or such and such a group must have hit my ball instead... Whatever. For those of you who would eliminate this penalty from the game I ask you; what is a fair alternative? If I hit my ball off the course and into somebody's kitchen window, what's a fair penalty? If I hit my ball so deep into the woods or long grass that it can't be found, what's a fair penalty? Stroke and distance is pretty fair if you ask me. Sure, there are times when I've sailed a ball deep into the fairway only to find that my ball is nowhere in sight when I get there, that's a bad break and you can't go altering major rules to account for that "once a year" situation (that could be solved by golfers properly identifying and only playing their own ball).
I think that the rules of golf have evolved quite well. Rules that were bad or are no longer applicable, have been removed (for example; In the past you couldn't mark your ball on the green which could effectively stymie your competitor [the 1913 US Open is a pretty famous example of this rule, Vardon effectively stymied Ouimet at one point during the playoff]. The rule was, and still is, just fine for match play but, for stoke play, it's unquestionably unfair and has thus been changed.). The evolution of these rules over time has resulted in a very solid rulebook with few, if any, holes that need addressing. If you like, we could discuss specific equipment and technology rules. I'm sure that would spark a debate on all sides.