Forum Moderators: phranque
PHP/MySql isn't as complicated (or restrictive), and programmers may find it easier to learn. Plus, some will say it's more efficient (running on Apache) than the ASP.NET platform.
Whether or not it's worth learning is difficult to say. I don't think .NET is going anywhere and it's always good to be diverse.
You'll probably want to look at Microsoft Certified Solution Developer (MCSD) for Microsoft .NET certification. You should be able to take the new Microsoft Certified Technology Specialist exams for Microsoft SQL Server 2005 and Microsoft BizTalk Server 2006 as electives towards getting your MCSD.
Good luck if you decide to do it.