I have been using PHP for webdevelopment for 7years now and I recently started using Zend professionally and I must say it works ok from my point of view. It should be easy to learn php with it. But it has some downsides too. Like skinnging of forms for example, is not as easy as it looks! There are also still problems with the form validations. Overall it's not bad, especially because it gives you much freedom of where to put your files and things like that. But to be honest, like I mentioned before, after those 7 years of php, I suggest looking at python (django for example) too. I don't say you shouldn't learn php, it's really great, but django just seems to have it al. Don't know about scaling though...