Lisa, I have a greenhouse that I wasn't really sure what I'd do with either, until after I got it. Like Woofie, I use mine for my seedlings in the spring and that's about it -- I actually start quite a few things under lights in the house first, then out to the greenhouse, then to the garden. This year I realized that I was kind of missing out because the way I set up the GH, I can't plant in the ground in there, and with our zone 4 seasons we're always trying to figure something out to cover stuff and keep it going longer in the fall. So this year I bought 2 "hoophouses", about 7 x 14 each, that I'm going to use for extending my season. We got them set up too late to get much advantage from them for the early season this year, but fall will be a different story (I hope!).
If you want to see (and read) more about that project, check out my "blog" forum on the Greenspace cubit; I've been trying to keep pretty good records and photos so I'll remember what worked and what didn't!
Once you start with a greenhouse I'm pretty sure you'll be hooked!
Sandy