Is an open source server in your future?

Version 4.0 of JBoss Application Server supports J2EE 1.4 and aspect-oriented programming. Developing applications in an open source environment is nothing new, but the mainstream acceptance of open source development environments is a relatively new occurrence that continues to increase. What application server is in your future?

[b]When it comes time to recommend your next application server, how will you evaluate your choices? Will an open source solution be your first choice? Why?[/b]