I use ATtiny85s, ATmega8s and Arduino. ATtiny85 is same as ATtiny45 that was used in article, but it has more flash memory (more than enough for small projects). With small package, low price and great performance it's great uC to start with.
Only sky is the limit when it comes to uC projects. For example it's possible to scan many buttons with one i/o pin by making voltage divider with resistors and using ADC (analog to digital converter).
There are lots of libraries to be used when interfacing some devices (like some LCDs (nokia 3310's display for example)), so it's easier to make something. After some time, it gets easier to modify those libraries, due the learned stuff.
And what comes to programming languages... I started with C then tried Bascom-AVR (it's like telling uC what to do, in english :P) and then came back to C. The real fun will begin shortly, when I start programming with ASM :D
One advice for starters: print (or draw) picture of you uC with pinout to paper, open texteditor (or AVR-Studio...what ever you use from writing your programs) to half of the screen and open your uC's datasheet to another half of the screen. This way you don't need to "surf" through the windows.
I've been thinking to make that USBasp for long long time... Maybe I'll make it someday, so I can use my eee from programming uC:s (except pics...still have to program them with desktop pc).
Hmmph too lazy to translate this to finnish... Hopefully everyone understands what I wrote. If you don't, just ask.
E: AVRFreaks's (link also in article, www.avrfreaks.com
) forums are great place to search AVR related stuff. Lots of tutorials, projects, questions and answers related to common and not so common problems... EVERYTHING and more.
Everyone who plays with uC:s raise your hand!
o/ -One AVR and pic user over here!