I'm glad this discussion was started--it's a very important issue!
I work with ATtinys because they're cheap and small, ideal for my projects (connecting them to RGB LEDs!). There's an unfortunate distinction between programming these chips with the GNU AVR toolchain (avr-gcc, avr-libc, avrdude, etc.) and programing Arduino boards.
The Arduino libraries can and should be made to work fine with any number of chips and programmers, without bootloaders and bulky boards. There's really no reason not to. True, different chips have different numbers of pins, feature sets, etc., but much of this can be abstracted and accounted for. I'm surprised it hasn't happened yet. It's very useful, as Arduino has all kinds of great libraries written for it that won't work as-is in the GNU toolchain.
It can be done in two different ways. The Arduino environment can be modified to accommodate other chip/programmer possibilities, or those of us using different chips can figure out the right Arduino code to include/modify to use without the environment. I guess we'll see what I get around to--the latter choice seems like less work!
Really, you should try Atmel chips without the Arduino board, it's cheap, tiny, and fun!