Personally, I worked with ZF since it was in version 1.6, and I am very pleased with it, I saw a very good improvement with 1.6, but I think that ZF lacks some ideas:
1- ORM, and later a very large implementation between ZF + Doctrine 1.2 gained very high popularity and I honestly rely on ZF + Doctrine in many projects and these days we can see a lot of integration between ZF + Doctrine2
2- a set of symphonies completely forgotten in ZF Do you think that the Zend framework does not comply with the Bundle Symfony principle? and I think it really is really soon to see (hopefully in ZF 2)
3- I had a lot of good points about symfony 1
- doctrine built in support - bundle principle - admin generators which can save a lot of time - symfony plugins is very popular - symfony documentation is really good
finally, I looked deeply at symfony 1, but I am very concerned about the noise of Symfony2 at the end of 2010 and until today its public preview of http://symfony.com/download and I have been trying to spend some time studying it.
I wish you good luck :)
Update I do not want my answer to imply that ZF is not good, or symfony is better than ZF, ZF IMO is a very powerful library and is a developer of ZF === an advanced + powerful PHP OOP programmer.
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