You can't assume that all aggregates are created equal. Amazon reviews, for example, are stupidly easy to buy. Youtube comments are generated by people who think commenting on Youtube videos is a form of expression; Yahoo! Answers are mostly Something Awful goons trolling each other.

You have to understand the motivation of reviewers, as well as their investment in their reviews. That pretty much makes Rotten Tomatoes wholly and absolutely useless (much like all movie reviews - ask me about the time I "wrote" a movie review for The Stranger). Tech reviews on Newegg or Amazon, on the other hand, can be evaluated on face value - "I hate this product because it failed this explicit, technical task that it had every reason to pass" vs "WORST PRODICT EVAR WOOD GIVE ZERO STARZ IF i COULLD" self-polices.

You trust the aggregate because you have no insight into how it is created. Therefore the big number matters. Sometimes, I use that approach: "I need USB cables. Here's a set with 8,000 mostly 4-star reviews. They probably don't suck too hard." However, my buddy is looking for fuel injection for his truck and I got a recommendation from someone who has put FAST systems on no less than 8 jeeps. Do I give a fuck that it's got like 3 stars most everywhere?

No. No fucks given. Gearheads are fucktards and gearheads attempting to use computers are shit-throwing monkeys.