Trails never really feel crowded, but Slaughter Pen and Coler can feel busy, especially on weekends. Bentonville is definitely starting to feel like a bike town. Just got back from a trip out West to several bike towns, and I feel like Bentonville had a similar number of bikes on cars and cruising the streets. Of course, the trails are IN Bentonville, so you have a lot of people cruising around directly in town vs. driving out to more remote trailheads.
Right now I really enjoy seeing all the people, because it makes the transformation feel so real. It's awesome going riding and meeting people from out of state every time I'm up at Coler or Slaughter Pen. It's also fun going riding and running into other friends and people you know while on the trails. Right now this is all really fun and enjoyable, but I also recognize that this can become problematic and annoying at a certain point when you're having to wait in line to drop in on a trail.
If you're outside of the immediate Bentonville area and in some of the lesser known trail systems (Fitzgerald excluded), then you hardly see anyone.