I used Boomerang for many months, their £3.50 service was just right for me.
I recently shifted over to Lovefilm, purely because I did a 30 day free trial for the promotional amazon voucher, then when that ran out found a 3 months for the price of one 'welcome back' voucher.
I used that on Lovefilm's £10.99 package, which boils down to £3.66 per month, and I get unlimited discs (one at a time), plus unlimited online film viewing via my PS3.
I'll probably go back to Boomerang once that 3 month deal is up, unless I find another 'welcome back' code to use.
In regards to Boomerang generally though, I thought their service was fair, I like how their list works and you can tailor it to suit you.
I was always a top 3 man, I don't mind waiting a few extra days to get the game I really want.
Pro tip: You can sometimes pick up epic bargains on the Boomerang used game store