Summary: I used to use Athlon 64 3000 and 3800. My concern was that this Athlon 64 3500 was new but more than few years old. I tested this CPU in my computer and found no sign of troubles. This Athlon 64 3500 met my expectations.
Summary: ...but I bought mine in 2004. The PC it went into sported outrageous specs like an NVIDIA 6800 Ultra video card, a 74GB Raptor drive (later updated to two in RAID0) and 1 whole GB of RAM (later updated to 2GB), all stuffed and wired pridefully into a Lian Li tower. Since then, I've bought two replacement computers. So as you can guess, it's a bit on the dated side.
Summary: OK, this 90 nm production AMD is getting close to 6 years old. Great for its day and age, great running XPPro on a backup rig. If you buy one be sure it's a Venice core as the design allows for massive overclocking. Earlier Barton's ran OK on Southbridge designed mobo's but really smoked on Asus A8V deluxe. Going price OEM w/o heatsink & fan as of 08/09 is around $30 bucks.
Summary: I've had this guy for 5 years and still hasn't let up. The little single core that could would be a good headline for this CPU. Comes 64bit ready which was pretty nifty way back when. Fairly low power consumption rated at 67 Watts compared to others available that are over 100W. Of course nowadays anyone looking to buy a socket 939 CPU needs to take a good long look at what they are trying to accomplish.
Summary: I've had this processor for 2 years now. When I bought it, it was already on the low-cost side. Two burnt motherboards (both ASUS, btw) and this thing still works. Great for office / Internet / basic videos. Works best without Vista. I never tried to overclock.
Summary: Overall I would say that if you are looking to build a good gaming computer that won't hurt your pocket and uses Windows XP this would be a serious processor to consider. But, if you plan to spend more than 500 dollars on all the parts, go with AMD Athlon X2 instead of this. If it weren't for the X2's on the market right now it would have been 5 stars.
Pros: 64-bit technology, Great L1 Cache (Wonderful for playing games), Even the Stock Fan and Heatsink keep the processor cool (Mine never goes over 42 C), and the Price to Performance ratio great
Cons: Old Technology (When I bought mine the technology was brand new but even today it's great for gaming), L2 Cache is not nearly as fast as the newer processors, not dual core