[obsessive1]

Personally, I don't mind when sites complain about my browser, as long as there is still an element of choice. Not all HTML5/CSS3 features are there in stable versions of a lot of browsers, so if your site were to use a feature only available in the latest stable version of Chrome, for example, and not Firefox, then I would consider that to be too restrictive.

However from the sounds of it, your application should work in the latest stable version of the major web browsers, which, in my opinion, is enough.

[ergo14]

Indeed, but i would find a common denominator - I would go with features firefox 3.x, webkit, opera + ie9 support. This seems like sane compromise to me.