[nebstrebor]

Around our shop (we have several PhoneGap projects) we frequently refer to Android browser as the IE of mobile. (and we're referring to IE6-8). Its crazy how many really key parts of HTML & CSS don't work on various versions of Android browser that are still very much alive and well, including some that worked on 2.3 and stopped working on 4.0 or 4.1. We basically have to turn our apps into static pages for anything < Android 4.2.

[underwater]

For me it's Mobile Safari. Everyone on the platform is forced to use it and it's many, many horrible bugs.