Never on the commute. The roads are far far too familiar for that, and given what I do "for fun", the commute is actually quite a dull pad.
When I first started commuting regualrly many moons ago I was a tad aprehensive, but as soon as I started doing 40-50 miles on big hills and dual carrigeways, a 4 mile hop on barely moving roads lost any kind of fear. Or interest.
Although I would add that nerves may not be a bad thing; it keeps you aware. Complacency and over-familiarity anywhere on the road is an evil thing which I will gladly attest to. I've had a fair few near misses where I've turned off for a second or two because of exactly this and I have to remind myself that although I've completed this journey safely and without incident x thousand times in the past,its no guarantee that I will at all times in the future.