Highly recommended. It's generally cheaper than off the rack, and of course tailored fits properly. Like anything, you get what you pay for though. The dodgy Indian blokes hanging around Tsim Sha Tsui pier are not the way to go.
You'll get an excellent suit for around HK
$4000, a pretty good one for $HK3000, and an average one for HK
If you're after a nice one, I recommend Linda Chow, 69 Peking Road, Tsim Sha Tsui. A little hard to find buit she's very professional and uses great materials. Make sure you've got time for three visits though, (measure, fit, final fit)