Yup, I commute on highways... the only roads my place of work is accessible from. Like you, I have wide shoulders, and it's actually quite nice for the most part. The one I'm on most actually has a shoulder about as wide as an MUP. In fact, I wonder why the shoulder isn't converted into a dedicated MUP - it's not like it would take a lot of resources at all. Just goes to show you how car-centric we are. The other one (the one my work is accessible from) also has a shoulder but it's narrower, though still wide enough. Traffic on mine are generally pretty low, though, but like your area mine has few bike commuters. I don't worry about what drivers think. Just be cautious around intersections and always be on the lookout for glass/etc... and also valuables like tools.

The worst part is the ramps - gotta be very careful there. Fortunately I think most people on my ramp (which leads directly into the plant I work at) probably know to look out for me. One hopes. Most drivers are very courteous, though I did have one truck driver who tried to command me to get on the "shoulder" (actually more like a bunch of broken asphalt). I didn't oblige, and he passed me too close for comfort, but at least not at high speed. That's the worst I've had to deal with.