I guess it is mainly the fact that it's not using CamelCase for directories, all lower-case filenames, underscores in methods and class names (_Task).

I am re-building a project in Laravel right now that I started with Slim, using a couple of Symfony components and own code and it's a bit of a turn-off for me that I ended up with quite mixed naming conventions now.

With so many PSR-0 compliant PHP libraries and Composer on the rise, I just think it's the way to go. This doesn't stop me from trying Laravel though and so far this is the only thing that kind of bugs me. But don't get me wrong, basically I really like it so far.