1. It's great for a one man show. Building an app takes a lot of time. I don't need to speed my time being a sysadmin. I want to spend it coding. I've used EC2 and a lot of my time was just spent tweaking and getting an instance working and making sure you don't lose your data.

2. The api's are great. I have instant access to memcache, mail, image and task queue apis, zero configuration.

3. I can build and test an app idea for free. If it gets traction it's already to be scaled.

4. I like Python. I used to be a php guy but after working with python my tastes have changed.

5. It's fast (most of the time). I do every once in awhile experience latency but no deal breakers.

Possible cons. 1. Technology lock in. Lets face it though, you're locked in with whatever stack you choose. If you get successful who cares, then you can hire so one to re-code your app if you desire.

2. Python and Java only, yep I can see this being a con. I had to learn Python to use app engine, which I don't think is a bad thing.

3. Terms and conditions. You are bound to their T's and C's

I'm sure there are more cons but in my situation I want to build an app quickly and it out the door. If it takes off I'm ready to scale and make some money:)