Parse is a Y Combinator backed startup that provides APIs so that Android and iOS mobile developers "don’t have to develop, deploy, or maintain their own server-side stack". They have just raised $1.1 million.
Parse allows you to save key-value pairs to the server and then later query them in relational database-esque ways. Parse also provides app push notifications and in the case of Android provides an alternative to C2DM that is particularly interesting in that it works on Android 1.5 and later (rather than 2.2 for C2DM).
If you are interested in giving it a go, TechCrunch have negotiated a limited number of beta signups.
Pricing hasn’t yet been announced but "will be free for small apps, and will scale up in a reasonable fashion for heavier usage apps and add-ons". The solution should scale as it’s based on Amazon EC2.
From a mobile developer viewpoint, it provides a quick and easy way to provide for the server side. It also provides backup of your data and an easy API for programming from the phone. One problem I can see is that you won’t have easy access to your data. While you can import via CSV, you can’t easily ‘see’ your data for reporting, admin or your own backup purposes. You will need to create an app do these things and access programmatically rather than via database viewing/reporting or CRUD tools easily created if you control your own server side.
Another downside is that you will be making your app dependant on the continuing existence of Parse. Hence, for now, it’s probably ok for hobby apps, trivial apps or apps with a known limited lifetime. Hopefully, in time, it will become self-funding or some large brand or company will end up using the service and will end up buying out or sponsoring it to guarantee it’s longer term existence.