Why a web-based emulator? Just use the one that's included with the Android SDK. You can simulate any combination of memory, screen size, screen resolution, and various hardware characteristics. Sure it can be slow, but it's getting better and is actually emulating the system you're developing for.
It's still slow because it literally emulates the phone running on an ARM CPU rather than simulate ala the iPhone simulator which runs an x86 version of IOS.
Yes I have. Admittedly we usually used real devices for testing but the emulator does just fine debugging most "fragmentation" issues (screen size and resolution and Android API differences).