This is the kind of question which occur when you check Zend framework homepage at the moment : First beta release is available since mid october '11.
As a fervent Zend framework user, i'm wondering when i should start upgrading, they also warn us that next ZF release 1.12 will help us in the process ot upgrading, but as i want to start a big project, not sure what's the safest path, any thought ?
If you have many projects that use ZF and don't mind deploying two versions, I'd recommend upgrading a smaller or less critical project to it. If you only have the one big new project that you'll be working on, there's more risk. You'll have to weigh the benefits against that risk.
Consider how soon this new project needs to go live. If you will be working on it in development for months, most likely all the kinks will be worked out of ZF 2 in that time. By going with the newer version which will obviously be released eventually, you're saving yourself the hassle of upgrading later. The code will be cleaner by starting fresh on ZF 2, and it most likely has many new features to shorten your development time. Of course, you'll have to spend some time learning them which offsets the gains slightly.
Finally, as Poelinca mentioned, you'll be helping out the community by testing it in a real world application. This is, after all, the point of releasing beta software. Given that even "release" software has bugs and goes through revisions, I think you're pretty safe jumping to ZF 2 sooner rather than later.
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