I just started using blockbuster's online rental service and I'd say it's alright. I usually get my movies two days after they send it out. it takes two to three days for them to receive a dvd and then it might take another day for them to ship out a movie. I sent out two movies on the same day and they were received a day apart though, that kinda messed up my schedule. their queue system is kinda weird(I've seen some stuff go from available now to short wait to long wait in a one day period and some of the stuff listed as on short/long wait got sent out before I saw them as 'available now'). I wish they had something built in to where you could interact with the queue more intuitively, like being able to actually drag titles up and down, but I guess that would be hard to implement.
I guess it depends on how you rationalize it. for example, you get two free in-store rentals(valid for dvds, vhs and videogames) per month. regularly they cost around ~$6, right? so if someone were to rent two games a month, it would cost them ~$12. for three more dollars, you get around access to blockbuster online's vast library of titles and you get to rent ~15(conservative figure) of those DVDs/month without having to leave your house, some of which are relatively hard to find/expensive. this is great if you're into niche stuff as some of it can be very expensive(for example, criterions go for ~$40 each retail). I generally don't like renting, but with next gen approaching and the possibility of $60 games, it might become more attractive.
I'm still not sure if I'll continue using blockbuster once my trial is up, although if I get a steady job I probably will as I want to support online rentals, I think it'd be really cool once they start to expand distribution centers so every big city has their own, although by then maybe the number of subscribers will bottleneck the service just as bad or worse than the limited distribution centers did.