Amy,
I have use Stevia for about 2-ish years now and after some experimentation, am very happy with it. I works GREAT for things like iced tea and hot cocoa, but it's also wonderful to replace most of the sugar in baked goods. It does work best in things that have their own, stronger, taste (chocolate, citrus, etc). You can also use it to sweeten things like stir-fry sauces, pasta sauces, barbecue sauce.
How much you use for any given item is a personal taste (it does have it's own very strong taste if you use too much and so you need to get used to it and adjust accordingly). Also, the different brands/types are all, well, different. I know big help, right? But it's so true. So once you buy one brand you might want to stick with it, but if you want to change, just be aware that you might need to experiment again. I think I use "New Naturals" or something like that, but I've also used SweetLeaf (okay), and Swanson's own brand (cheaper, not as good or strong as New Naturals, and another brand that you can buy in bulk (was very tasty, but very strong).
Hopefully Kathryn and a few others will chime in here too!
Let me know if you have any more questions
Mattea