Heck, I had an extra two hours to spare at CLK and went into HKG for 2 hours last weekend (and I'm there every 6-12 months anyway).

The airport express train takes only 23 minutes from CLK to Central and only 20 minutes from CLK to Kowloon. Trains run every 10 minutes or so. Buy a SAME-DAY RETURN ticket which costs the same as as a one-way ticket. HKD80 to Kowloon and HKD90 to Central. Critical difference is that from the Central station, you can actually walk out into the "city" whereas from Kowloon station, you definitely have to take one of the shuttle buses.

What I would suggest is the following. Buy a same day return tix to Central but get off at Kowloon station, take a shuttle bus to the Holiday Inn Golden Mile, the Hyatt, or the Jordan MTR station if you want to take a nice long stroll down (south) Nathan Road.

Have dim sum or breakfast/lunch at a hotel restaurant (unless you speak Cantonese, going into one of those cavernous restaurants will be a challenge but the food will be pretty good). Take a look at some eyewear at the many optical shops. Haggle down the price. Reach the southern end of Nathan Road and walk towards the HK Science Museum and Cultural Center Complex (maybe check out an exhibit). From there, there is a nice promenade with a view across the harbor of Hong Kong Island. That's assuming of course that the haze and pollution don't wipe out the view. Oh yeah, it's going to be hot and humid already in May, so wear light natural fabrics. Shorts and sandals are fine for casual wear in HKG (although you may feel uncomfortable if you want to visit some of the upscale boutiques across the harbor in Central).

After taking a stroll/walk along the promenade, make your way over to the Star Ferry terminal. Take the ferry to Wanchai for about HKD2.30. Ferry should take about 10 minutes to cross and another 10 minutes max wait. From Wanchai, you can walk or take the tram (HKD1.50 or HKD2.00) and slowly make your way toward the airport train station in Central (the station is called Hong Kong Station and is accessible from the Exchange Square complex of buildings or via the Central MTR station), passing by the major architectural landmarks in HKG such as the Cheung Kong Building, the Bank of China Building, and the HK Shanghai Bank Building. If you were short on time, you could take the ferry from Kowloon to Central directly and then take a 5-10 minute walk to Hong Kong Station. Very easy overall.

Major shopping complexes on the Kowloon side include Harbour City/Ocean Terminal (next to the Star Ferry Terminus), while two other big ones are Pacific Place in Admiralty/HKG (also next to the Conrad Hotel) and the Landmark Building in Central/HKG. Upscale boutiques in all three. Mass merchants in the first two as well.

As per Randy's suggestion, Shanghai Tang has several locations, including its flagship on Pedder Street in Central (there's also one at the airport and in NYC).