I ride a trike every day to work, and I feel safer on it than I ever did on my DF Trek. Cars give me more room. I can't get knocked off by anything. Weaving is out of the question, though (and very dangerous, even on a regular bike!)
It's pretty tricky to transport a trike by car; unless you can fit it inside or in the back of your pickup, there are only a few racks available that will accomodate a trike. Transporting one on a bus is almost out of the question.
Locking up is easy; I usually just attach the rear wheel to something secure. My trike doesn't actually have any triangles, so it's difficult to secure the frame itself. Other designs are a bit better in this regard.