GPS bike computers in track cycling?
In track (velodrome) racing, visible cycle computer displays are generally not permitted. So the only funny looks will be from the commissaire who will request it be removed. 

This is the UCI rule:


  UCI CYCLING REGULATIONS TRACK RACES
  
  3.2.005 Riders may carry no object on them or on their bicycles that could drop onto the track. They may not bear or use on the track any
  music player or radio communication system.
  
  In addition, any electronic device with display (for instance 
  speedometer or powermeter) must be hidden to that it cannot be read by
  the riders.


My track bike has an SRM power meter and SRM Powercontrol bar mounted computer. The display may only be used in this manner for training. I used to use an under saddle mount for racing so I could still record the data. In the early days of this rule being implemented I was able to use a cover on the display to comply but that soon gave way to no devices permitted on the handlebars. Then we started to put computers on the top tube behind the head tube, and that was frowned upon as well. So we moved to under saddle mounting sort of like this:



GPS is of course useless on indoor velodromes, and not that great on outdoor ones as its resolution when changing direction is not that great. If you ever look at the map plot from a GPS device of a bike ridden around a tight enough curve at a decent speed, like on a velodrome or descending a twisty road, you'll see the track plotted by the GPS data cuts the corners. Speed is assumed to be the straight line distance divided by the time interval, when actual distance is around a curved path.

This is why on tracks we prefer the use of wheel speed sensor. Better precision, resolution and accuracy in wheel speed measurement. Of course wheel speed on a velodrome doesn't equal bike speed, since the wheels travel a different path to the rider (wheel follow a larger radius arc due to the lean angles involved in riding on a track).

It's possible to compensate for this with some maths and knowledge of the track's geometry. It sort of depends on what you need the speed data for. e.g. for aerodynamics testing you really want to know the velocity of the rider relative the surrounding air, and not the speed of the wheels since it's the rider that makes up the bulk of the aerodynamic drag.