There are a few studies existing that check the involvement of the community into an open source project. The code quality varies a lot, and usually community patches do not find their way into the main source code. Sometimes the patch is very good but the style is just not the taste of the core developers.
With symfony I now noticed an area where the real power of community contributions unfolds: Translations.
Fabien created an initial translation of the new symfony admin generator from English into French.
Within 48 hours we have received 25 additional translations. I am pretty sure that shortly we will have covered all the main languages used on the net. This is great! And I think a key contributor to this is that basically everyone can do this. There are no real quality issues with these contributions, as translating to your native language is pretty easy. Also the amount of work involved is very low, and no extra tooling is required to translate. Its just easy.
However there are two issues with the translations:

  1. How to deal with updates?
    With every change of the base file all translations would need to be updated. Falling back to english would be ok but not nice.
  2. How to deal with conflicts/possible nonsense?
    The problem arises from the fact that the core developers cannot read the translation. In worst case there could be written: “this project sucks”. And what if there are two contributors contributing the same file with different content? Perhaps the best solution would be to do a quick Google Translate check and see if the contribution makes sense.

But even with those small obstacles in the way, using the power of the community is very suitable for translating small chunks of text into other languages. It works well!