As always with file sharing the more you have to give/the more people you know with more to give will get you better results. It used to be if you knew where to find the online emmm sites, and how many good FTP connections you had. Then napster came along and revolutionized that with P2P sharing, but even napster used a centralized "hub" (and not just one).
They died because of it, oh well, but still I don't think the massive "everyone connected to each other" networks are very efficient, inc. kazaa, gnutella, winmx, ect. There are good at making the statement "you can't shut us down" yes, maybe, but its hard to find quality sources, or rare shit. Supprisingly its a lot easier to find "rare" things, and downright easy to find ISO's/ movies/large things in a more compact group of users, say only 1,000 or so, on a better program. My favorite for this is direct connect (use DC++ for a client) but there are others. The ease and quality of finding/speedily and reliably downloading stuff makes it worth the slightly harder setup and location of initial sources (its not that hard, takes like 5 mins more).
Advantages:
Speedy Searches (doesn't take 20 mins to start getting decent results that reflect whats avalible, only takes 5 seconds)
Better content (for many reasons, one being the ability for closed groups to moderate and impose requirements
Faster sources are easier to find
More control over what goes back out, and how stuff that comes in comes in (although DC++ still doesn't give me the ability to do split downloads, boohoo) Aka more features.
Disadvantages:
If yer on 56k you can't even get in to most groups.
Its moderated, if you don't have anything to share you can't get in to the good groups, and you can't share crap even if you want to.
Takes time to find the good groups.
From experiance the private groups are the best, on one with only 400ish people I can find anything I possibly want, and the average share per person is 100GB with 25k of avalible upload bandwidth (on average). Ok, theres my advertisment for smaller group software over the massive P2P's, since no one else had mentioned them much (stezo).
The best thing to do would be to use all the programs, each one for whats best suited to it.
And BitTorrent Fing rocks.