I did a gap year in 1999-2000 through YINI (see someone else's post) and then went on to do my degree. I've just completed my penultimate year of uni and am flying in a Uni Air Squadron loving every minute.
My gap year was with an insurance company and I study Economics now.
KEY POINT 1: The management experience/ team skills I gained in my gap year aided me greatly in getting on the UAS and being a better leader - the clincher to doing well at a BA assessment centre or OASC - the subject you study or whether your gap-year was relevant to flying doesn't matter IMHO.
KEY POINT 2: Back in 1999 when I took my gap-year the employment outlook for cadet pilots was great - BA, BMI, AMM etc.
Now it's awful, so maybe if you do a gap year by the time you graduate it will be great again?
BIASED POINT: Take advantage of the opportunities provided by UAS at uni - who knows, you may decide flying Eurofighter and drinking the cheapest beer in the universe is more exciting than programming the FMC on an A320 all day!