My system is a micro. No problems here.
Right now, all of my PCI slots are open. I removed the modem, well, I had a reason at the time, but I forget. My graphics card is AGP. I am using onboard sound. So I have three empty PCIs.
Using a micro is just up to personal choice.
Oh, and Nukem, there's no way you could put an ATX board in my case, as it is a micro case as well. Besides, the smaller cases are really cool.