Yeah, the layout certainly takes some getting used to. I've been trying to learn how to do things programmatically for the most part. It can certainly cut down the time it takes to design the app's UI.
The emulator is slow seemingly whatever computer it runs on. I'd suggest getting an android phone if you can, as it runs much faster on an actual device (though when running in debug, it will always run slower than when not in debug mode).
As far as the l/m/hdpi folders, I still only use m. I just don't want the app to be bloated with extra image files. Most files stretch, and look fine. I suppose if you're going for absolute quality, you could include 3 versions of each image file (one for each screen density, not to be confused with screen resolution). I've found it's not necessary in most cases.
One big pain in the ass when designing the UI for android is that there are so many screen sizes, with a few different aspect ratios. So far, what I've gone with is to design on one screen size, and have everything resize using multipliers of the screen size. Most of the time, you can just use fill_parent, and creative use of linearlayouts though.
While I'm no expert yet, if you have any questions, feel free to PM me. I've been heavily into eclipse, and the android SDK for a few months now.