Using a laptop as a timing device has advantages and disadvantages. The advantages are ease of use, and if anyone wants to take on the challenge of developing the software, inclusion of optional start instructions (e.g. "Follow tapes for 100 metres to the start triangle blah blah blah"), which guarantees consistent instructions to all competitors, and relieves start officials the tedium of repeating the same instructions every X minutes for 2-3 hours.
The disadvantage is drift in the PC's clock. Unless the PC that is used has been calibrated against a reliable chronometer, the possibility is that times may be unreliable (probably OK if SI start boxes are used for the actual start and the PC is only used for the approximate start time).
Our club uses an Alge Startbeep, but an addition to the range also looks quite useful (have a look at "startbeep" and "start clock" in the product list at
http://www.alge-timing.com/alge-e.htm)