Just make the freebie permanent
I'm playing around with a site/mobile app idea right now. I have no idea whether it'll take off, so I don't really want to stump up a load of cash. Both Amazon and the Google App Engine have tree tiers that mean I can keep playing around with it for free until it gets popular, if it ever does.
Free until September is great, but I'm still not going to go for it until I get a longer term promise than that. Just make the smallest, lowest tier available for free, for good. Then more small startups will start using Azure.