I believe something is beginning to happen... down at the OS level, Red Hat have absolutely made big in-roads, and in middleware (esp the Java world) you have Glassfish & JBoss doing very well, and MySQL and PostgreSQL have certainly begun to penetrate the enterprise. And higher up the stack, you have Zimbra, SugarCRM, etc.

No, SAS, SAP, Oracle Apps, Lotus Notes, etc., won't be going away tomorrow. But I think there are clear signs that acceptance of F/OSS in the enterprise is growing.

For my own part, I'm working on an Open Source startup, playing in a space similar to Jive or Yammer... so - for what it's worth - I've bought into the idea. (Then again, I'm a F/OSS ideologue, so I'm not exactly unbiased).