We have been testing the MySQL RDS Service from Amazon here at RF, and so far it looks good for what we use MySQL for. We don't have that much data left in MySQL though, but some of the services are still mission critical, and we have had a couple running on RDS for a week or so.
I have to say I am pretty happy so far, but there are a couple of things you should know before you use the services. To begin with, you don't get a proper MySQL root account, i.e. no SUPER privileges. No big deal I guess, but this means there are a few things you cannot do. I was planning to migrate off the EC2 based server to RDS by setting up the RDS service as a slave, and then switching to the RDS service, but as SUPER privilege is required for CHANGE MASTER TO, I could not do this. And before you ask: Amazon DOES support slaves among the RDS servers, but this is set up using their own methods. Easy to use, yes, but not as flexible as the real thing.
As for parameters, you can modify a bunch of them, but not all. I have to benchmark performance here eventually, but it has been sufficient for our modest MySQL needs so far, so I might not even do that. I also have to check what parameters I am allowed to modify and which I can't in some more detail also, to figure out if there is anything significant missing.
So far though, I think the conclusion is that this is a great service for people with low / medium requirements in terms of MySQL. Backup and snapshots are a breeze and are automated, cross availability zone use is also an option (not tested by me though). The server is accessed just like any other service, so you can set up Route 53 with a more reasonable name to point to it, if you wish. Which nodes can access the server is also controlled by you, both the service itself controlling what can access it, and by the usual MySQL GRANTs.
When we get more servers running on RDS, I'll let you know more.