I moved to a platinum card just recently, and have had mixed results. I wasn't sure what they did or didn't do, so I have tried them out with a few things.
1) I asked them to research solar hot water systems for me, and arrange some quotes. I thought it was a long-shot that they'd do this, but they didn't seem taken aback. They did quite well with the research, and emailed me info about three different systems, but didn't really follow through with the quotes (I ended up arranging them myself). Still, this saved me a few calls so I was happy.
2) I asked them to recommend a local hairdresser in either the city centre in Canberra or in the area I live, and make an appointment for me that week if possible. They emailed me details of four hairdressers, one of which was in the city centre as requested, two were in other far-flung suburbs, and the third was in Brisbane! I asked them to go ahead and make me a booking for the first. They weren't able to book me in that week, so I ended up calling myself and booking at another convenient time.
3) I asked them to find a hotel room in Adelaide for me, after I'd first checked out what I could expect booking through Wotif. They admitted that they mostly just check the prices on Wotif themselves, but I think it was still worthwhile: they saved me the effort of trawling through the long list of available hotels trying to work out which looked nicest for the price. They suggested one that looked good, and I booked it myself.
4) After checking out car rentals online for a Brisbane trip, I called to ask if they could get me a rental at a better rate. They did, and the rate they managed to get was better than the discount I could get through the Entertainment Book, and also came with a free upgrade. Next time, I'll probably just go straight to the concierge for this.
Apart from one or two deals that they have with hotels and rental companies, my impression is that they basically just search online for whatever you ask about, but it can save some legwork.