I've been thinking about replacing Netflix with Amazon Prime but I'm not sure what movies fall under the 'Prime' label. Is it any 'Instant Video' or is there another sub-category that I can't see without having Prime?

If it is any 'Instant video' then I'm definitely going to go for that, just for the large selection but if not, I might as well stick with Netflix for the android app.

 

It's not all of the instant videos, but it does include a good chunk of them. In general, you miss out on the newer releases (Hunger Games is the newest movie on Prime right now, at least that I noticed). Downside is no HD unless you stream with your Kindle Fire, Xbox, PS3, Roku etc.

You also get free 2-day shipping on anything sold by Amazon (and a lot of their partners as well). I have it primarily for that - it pays for itself with the number of things I order on online.

Edit: If you're curious what the Prime selection is like, you can see it without being a member. They also have a free 30-day trial.