Zend

What do you like best?

Zend is very good for complex projects. You can easily use it and scale it and do not mind about size of the project and years that it will be supported. As much as using it, more you get.

What do you dislike?

Currently there are not many developers working with it and it is not easy to find appropriate resource. Also Zend has added complexity. Very strong learning curve. You cannot just jump in and start using it smoothly. It will be a very hard path. Architecture is very important as well. If you do wrong architecture of the solution initially, then everyone will suffer all the way.

Recommendations to others considering the product:

Use with care, maybe your project do not need it and you can use something lighter. Do proper architecture from the very start. Find proper resources who have already worked with Zend. Be prepared to have a long way together.

What problems are you solving with the product? What benefits have you realized?

Zend is optimal to write perfectly custom solution for big business. It can solve almost any problem and everything can be achieved. Huge benefit is a Zend Studio. You get your development environment right out of the box! It is set up and allowing to work smoother. Another huge benefit is a good documentation and wiki with tutorials videos and everything. Don't forget about community that is ready to help. Final point: it is open source, so you can jump right into source codes when needed and find everything you need.