Lack of persistent disk out of the box and IP addresses that are not preserved between reboots are indeed the 2 primary issues that make hosting public web sites on Amazon EC2 "tricky" (even though not impossible).Instead of addressing the problem head on, have you considered multisourcing your infrastructure? Let Amazon EC2 host your highly scalable computationally heavy logic, but host database layer and possibly thin static IP layer somewhere else. I described our multisourcing technique called VcubeV in my article in February 2008 issue of Linux Journal - www.linuxjournal.com/article/9915 .
With database writes way less frequent than reads and availability of excellent caching (memcached, for example), this is quite doable.
UPDATED 3/27/2008: This post is no longer entirely accurate. Please see http://aws.typepad.com/aws/2008/03/new-ec2-feature.html for more details on availability of static IP addresses in EC2.