I'm looking for advice on what best technologies to use to build web apps/sites with the dynamic, social networking, user-interactive-type functionality seen on sites such as YouTube, Flickr, MySpace Hot or Not, etc. I'm currently Looking into using Apache (free on OS X), MySQL, and PHP. I just installed MySQL and Navicat and enabled PHP and Apache on my MacBook to play around with. Is this the best path to take for what I want to do? Is the learning curve way out there? Are these technologies worth spending the time to learn? Are these skills marketable? Will these technologies be around for years to come? Or are the newer and better technologies to look at instead? Also what should I use for the web pages? Flash? Ajax? CSS? I would like all site code, databases, etc to be cross platform - I prefer running under Mac OS X, but would like to easily run sites from Windows / Linux servers if ever necessary. What GUI tools are available to help with all this... for database design and management, middleware (PHP) coding, web server management, webpage design etc??? I would like to develop on OS X. About 8-10 years ago I was heavily into building dynamic sites with Lasso, FileMaker and WebStar - all running and developed on Mac OS 9. These technologies were very easy to work with but I have the feeling they wouldn't handle a huge site such as YouTube, Flickr, etc. Are there pre-made solutions to do this that would save a lot of headaches? Or am I better off building it myself??? Any advice would be appreciated!