There's a few oddities that come from the custom UIs, which make it kind of annoying if you want to design a good looking, consistent-with-the-rest-of-the-phone experience. Admittedly, this isn't a huge problem, and indeed is only a problem with a few of them (Sense UI, mostly), but since almost every manufacturer has a custom UI, it can be a pain.
I don't understand this point. I have an HTC Desire with Sense, i downloaded a bunch of apps from the app Market over the last few weeks, and I never noticed any differences in UI between the build-in spps and the ones I downloaded.
Have you ever had to make adjustments to your apps to make them look good/OK on, e.g., Sense? What kind of adjustments were they?
I hold the same questions, both as an Android developer and as a Android app consumer -- Sense plays zero part in my development, and as a user while it changes the home screen and offers some widgets, it does nothing to change individual apps. Nor does Motoblur, or Sony's Rebecca or whatever they call it, or LG's....