Got to agree with Penko's post. If you've planned on a certain speed for decent and then get asked to slow down it will put you high on profile and some pilots hate using speed brakes. Personally I just advise that I'm unable to make the restriction, however as NOD says it can sometimes take a while to get a word in edgeways. Secondly as someone else pointed out, jet aircraft don't go and slow down. If you allow it to do a little bit of both it will take a while to reduce speed.
The biggest time that I'm guilty of not adhering to ATC assigned speeds is the 160 to 4d request. The aircraft simply will not slow down without dropping the gear. Very often it ends up being 170ish in which case I'll drop the gear at 6 miles and be reducing through 150 by 4 miles. (basically too fast for the first couple of miles and too slow for the last couple of miles). Not strictly correctly but I believe it evens out correctly. The alternative is drop the gear when requested, p**sing away loads of fuel and making lots of noise. Of course if the speed is ridiculous I will drop the gear early.
Standing by for abuse
