I spent a day at Phil's Area, in Bend, OR. Phil's is right outside town and is the primary trail system for quick lunch-time or after work rides in Bend. The trails are flat and buff with good flow but little interesting. I imagine racing them on a hardtail would be fun, but coming from downhill terrain I was pretty bored.
I rode the Larch Mountain trail NE of Portland a couple times and had a blast. It has great flow and fun obstacles but nothing scary. The area is a bit of a maze; we started climbing to a peak. The top couple hundred yards are covered in babyheads a couple layers deep, but below that the trail is in great shape. It switchbacks down quite a ways to Cold Creek, then runs beside the creek for a while. I imagine that there are a bunch of other trails in the area, but avoided them for fear of getting lost.
We also spent a day at the Mt Hood Ski Bowl. There's one really good 4 mile XC trail there (Optimator?), but otherwise it's not worth the drive, and certainly not worth the lift ticket. Their double-black trail is just a lift access road with some off-camber loose rock - not easy, but also not fun. The lower switchbacks trail doesn't flow quite right, while I enjoyed the lower technical trail my friends did not. I think part of the difference was that my bike is built up a bit heavier than theirs are, so I had better traction and control. There was lots of fall-line deep dust, so they drifted around quite a bit.