I used to only do the one entry per request thing too, until I had a sponsor turn me down for a review/giveaway because they "require" at least 100 entries per contest to make it worth THEIR trouble. That was simple enough - I allowed extra entries for doing the extra things. But then I keep hearing that folks don't really like all that. I know that I myself am disheartened when I find something I'd love to win in a giveaway on another blog and there are already 1,500 comments halfway through the giveaway!! At that point I feel like I'm wasting my time entering that one at all...
I am tempted to go back to the one entry per request thing. But then that looks like all my giveaways are "low entry" - which does prompt some casual surfers to enter, but it also looks to the sponsor as if their giveaway isn't drawing very much attention on my blog.
It's a two-edged sword. :-/