so you may find yourself having to adapt Arduino code
With the advent of Digispark and Trinket, a lots of code has been adapted to the Attiny85.
But it's not plug-and-go like any of the ATMega328 boards available, and the documentation sucks. For example it took me over an hour to get TinyDebugSerial working on a Digispark. One of the few pages I found covering it is here:http://www.ernstc.dk/arduino/tinycom.html
However that page says output is on PB3 while it's actually on PB2 when F_CPU is >8Mhz.
The micronucleus bootloader is a hack job (and Jenna Fox doesn't deny it). After 15 days of going through the micronucleus code I barley understand how it all works, while understanding Optiboot only took 15 minutes.
I haven't been able to get nRF24l01 modules working with the digispark which is an example of the kind of problems you can expect to run into. Part of the problem is specific to the ATTinyx5 (USI instead of SPI on the ATMega), and part is because 2 of the 6 available ports on the Digispark are crippled by the USB pullup resistor and zener diodes.
Eric pitches the Digispark as a beginner-level plug-and-play arduino compatible device. Just download their patched version of The 1.04 IDE and go. But the IDE isn't well patched. Look in the libraries directory and you'll find Arduino_SPI instead of SPI85. Although you'll find TinyWireM_Digispark, there's still a copy of Arduino_Wire to make things confusing. Both Arduino_SPI and Arduino_Wire should have been deleted from the Digispark version of the IDE; something that's really simple to do but wasn't done. I suspect it is so Eric wouldn't keep his kickstarter supporters waiting.
With some work someone could make a decent Tiny85-based Arduino. Patch the IDE so all the compatible libraries are included and the incompatible ones removed. Have it emmulate a USB serial port connected to a STK500 compatible bootloader, and include a fully-compatible version of the Serial class. But that's a lot of work to save ~25c (cost difference between the Tiny85 and Mega8A), and with the upcoming availability of the LGT8F88A, I think we'll see that cost gap get smaller.
I'd say the trinket is well named. They're more of a cute toy than a practical hardware platform, and they're more than double the price of a Pro Mini ATMega328 board. I plan to give my DigiSpark to a friend who likes cute electronic toys and do my hacking on Pro mini boards.