How many people here generally buy used?

Some of each. Used comes into play when I couldn't afford to buy new.

I used a number of factors to determine if I purchase used or new, including: 

How good is the deal?  If used is 5% under new, I'll just go new.  If I can save 30-40% used I'll go for it.

How often does the product pop up on the used market?  If it takes a long time, I usually loose patience and buy new.

Does it have a lot of moving parts?  E.g. a complete turntable vs an amplifier.  If there are lots of bits that can break I will lean towards a seller with a decent reputation.

What is the state of the technology?  If it's a class A or AB amp vs a class D. I'd go used for the A/AB and new for D because that tech is still evolving.  DACs are a similar example.

Mark

Eh, kinda 1/2 & 1/2, but I like trading gear too. 

Mostly used about 80% except for tonearms and cartridges those I always buy new.

"How many people here generally buy used?"

Only two items were purchased new. Oddly both of them preamplifiers. A Yamaha CX-2 and recently a BHK. 21 years apart in time. Maybe that provides enough time for one new purchase?