I have been working with the predecessor of ATTiny2313 -- the AT90S2313 -- for many years now and it has been a GREAT chip. The on-board serial comm and SPI are very helpful. I also like the AVR assembly language, which was pretty easy to learn. I have worked with their small 8-pin chip (ATTiny25) a little but unfortunately, it is limited.
Guys, you've been talking about Atmel stuff, which is good, but.. there is something better, somewhere else.
For the real fun, give yourselves a try with the newest Renesas RL78/G10: http://am.renesas.com/products/mpumcu/rl78/rl78g1x/rl78g10/index.jsp
Or for something more beefy, look at the RL78/G12: http://am.renesas.com/products/mpumcu/rl78/rl78g1x/rl78g12/index.jsp
I am just talking about something comparable to -or even better than- the ATtiny pricewise and which comes in low pin count packages, but which renders ATtiny in the dust, starting with the 16-bit vs. 8-bit capabilities, power consumption, etc...
Great thoughts Jeremy. I think a lot of people are starting to crave the hands on approach and finding the arduino to be a peculiar fit. I think this could be the post that encourages many of them to just re-connect with their roots and jump into ATtiny!