I was asked several years ago by a family member to put reflective tape on my bike. I refused for several reasons:

1. Tape encompassing the top tube, would constantly cause friction with the rear brake cable
2. Tape encompassing either down tube, would cause friction with the wheels.
3. Tape on the handlebars would decrease the effectiveness of the handlebar tape already on the bike
4. Tape on the spokes would cause friction when running my bike lock through the spokes to lock it up.

I use lights(not reflectors) instead.