Microsoft SQL Server Developer Edition Is Now Free
blogs.technet.microsoft.com
blogs.technet.microsoft.com
Anyway the license administration is the absolutely worst thing with SQL Server, which is a shame as it is really a great database.
At what workload levels does engine quality come into play? So far I've thrown multi-terabyte/high TP workloads at Oracle, Sybase and DB2, and they've all gotten the job done with a minimum of fuss. This leads me to think that there's really no reason to look at databases as anything other than a commodity service which should be chosen on the basis of cost.
Postgresql is good but lacks some of the polish and features of the paid for databases.
Availability and cost of skilled staff and compatibility with existing deployments might also be important. So not critical differences perhaps but squint hard enough and you'll see there are differences nonetheless.
(unfortunately looks like this article was flagged so we won't see the conversation that would have come from it :( )