Lot of interesting stuff here. Let me address them out of order because - well - its Friday.
First off: MySpace was built badly. All languages allow you to develop badly. That isn't a CF or Java or PHP issue - it is true for all languages. The creators of MySpace have gone on the record as saying they simply wrote code and threw it live w/o testing. They did this so they could quickly get new features up. That ISN'T an excuse for them - but it explains why their site performed so badly.
Shelly - I think most folks would tell you to work with the language you are most effective with. If you are effective with ColdFusion, then you should use it.
Job Market: Learning just ONE language would be a bad idea in general, no matter what the language. The RAILS folks like to talk about how hot their language is now - and it is hot - but it doesn't make sense to base your career on just one language. I've been using ColdFusion for 10 years now and while it is my primary language, it is not my only language.
Flex: Flex is a language to generate Flash. Totally different from CF or PHP.
Adobe: Adobe is VERY much behind CF. Version 8 is being worked on right now.
Cost: Anyone who ONLY considers the cost of software is making a mistake. While software cost is a concern, so is development time and support. One of the benefits of CF is that it is one of the best languages for RAD when it comes to web development. I am obviously biased, but outside of that - you don't just base your decision on one cost - but factor in everything. That's why I use OSX and Windows over Linux - they are both just easier to use, setup, and support than Linux. Also do not forget you can run a 100% free version of CF on your desktop for learning. When it comes time to deploy your application for your client, plenty of ISPs support CF, and at very affordable costs.