Drupal is my favorite PHP framework. It is has a very developer-oriented community and supports many great and powerful features right out of the box. It also doesn't force you to reinvent the wheel (form validation, success and error messages, http response code handling, logging, and so on). It is "opinionated" and I like it that way.
I dislike Zend for many reasons, but most importantly it's very difficult to discern what the "right" way to do anything is, and choosing poorly will typically bite you in the ass later. For example, not using the Zend menu system will cause trouble when you want to make a breadcrumb or do translation. Random internet blogs may get you to *some* solution, but usually not the correct one. The Zend form system is extremely convoluted compared to Drupal.
A caveat: there is definitely a learning curve to Drupal. Less so than Zend in my opinion, but you will definitely have many new things to learn before you will be efficient. Unlike with Zend, the correct way to do most tasks is well-documented in Drupal and has examples.
I have a CS degree from a major university. I have to disagree with most of the comments I've seen so far. Things like design patterns, proper object modeling, even advanced data structures and algorithms can be picked up on your own with a bit of effort as you need them, and experience building real production used software is the key to hone those skills.
The "with a bit of effort" portion is key, and from what I've seen more people will not go back and fill in the gaps in their skills (or at least well). Industry experience is also very valuable, but will rarely cover the same ground as someone with a formal education and a couple years experience.
Any given program will expand to fill available memory.