I will start a POS (point of sale) system that will begin as a regular intranet system (in his initial-beta stage) but I want to scale later to a cloud offering. I will offer it as a hybrid solution.
I want it to use firebird, because the easier deployment, minimal footprint and the ability to use a embedded multithread server. However, I worry if firebird could be used for a cloud service with fault-tolerance, data replication, etc... to be reliable enough to small companies put his business on it (similar to the service of freshbooks).
My other option is use Postgress, but I have not experience with it.
Is FB good enough to be use as SAAS backend? Any successfully implementation?
P.D: I thinking on deploy it on GoGrid or Rackspace...
FB is a great option and it can handle large data sets and has the ability to span a db across multiple files . I've been using it in a couple of web projects most recently on inmobiapp.com. But the one thing I see lacking is replication, so far the only solution I've used is called ibpreplicator it's a very good rep. tool if configured properly. You can try it for free but you have to buy a license.
Also consider driver support for the programming language you will use. Last time I checked FB on Rails support is not that good on the other hand PHP has great support for FB.