Citygate's I.T outlet was a fantastic place for me. I went two weekends in a row this May. Wish I had bought more stuff the first time around. Got my hands on a killer APC coat for $2000HK and two very nice wool sweaters for $150HK each. Obviously nobody in their right minds would wear those in summer in HK, which is why they were so heavily, heavily discounted. The second weekend all sweaters and winter wear was GONE. Slim pickings now for anything of a quality material. For ladies, the I.T store had a crapload of designer dresses and blouses, so that may be a good reason to go.
If you need basic T shirts, I'd say check out the Bossini outlet there as they also had some very good deals (but their stuff doesn't fit my small frame well).
There's another I.T outet store at Tsim Sha Tsui's Silvercord Tower on the 3F. Don't go into the 1F store expecting sale prices. It's all happening on the 3F.