I've used EC2/AWS and google AppEngien (java) for sometime. Using amazon is great, fixable, configurable and pretty stable (IaaS). AppEngine is good two, but comes with extra services (PaaS): such as shared login service (user service), image service, law level infrastructure management: you don't care about operating system configuration, database clustering, snapshot and backup etc. You can achieve some of these with SDB in amazon solution, however, you still need to worry about number of instances up, and to configure / install and prepare your instance.<p>In Google, they limit you to the technology you should use, and they will for sure remove a lot of the library such as IO or at least limit it's scope which result in great constraints. Interacting with the database is another challenge: in google it limits you to bigtable or you should remotely use database in the cloud such as interacting with amazon SDB. Google: they don't have SLA, or do they? How can i as a business relay on their service? I'm just thinking loudly, any ideas guys? Any other interesting cloud vendor? And why?