I was testing Arduino with new laptop running Windows 8.1. So I hope I could easily get the boards detected by the OS and get the IDE installed without too much problems. I had earlier read reports on new Windows 8 security things making Arduino driver installing hard. There are even video on solving installation problems. So I was expecting some problems.
Before installing the IDE itself, I tried fee of my Arduino boards how they are detected by Windows 8.1 system. The Arduino boards should be detected as USB serial ports when plugged in. First my Arduino Nano clone (used CH340 USB-serial IC) was detected well. Next I tried a Arduoino Duemilanove (FTDI USB chip) and it also worked well. So did Duemilanove 2009 Atmega 328P SCM Board.
Then I tested Arduino UNO, but it was not correctly detected due lack of suitable drivers. The next task was to install Arduino IDE (Arduino 1.0.6). Installation went well. At one point I needed to give permission to install the driver. Everything worked smoothly, and after that installation my Arduino UNO board was correctly detected. Drivers seemes to also cover Arduino Leonardo.
So things went better than expected. Installing Arduino to Windows 8.1 seems to be nowadays pretty smooth process.