Just booked my second trip through the Citi Prestige concierge.
I emailed them asking for a quote for 4 hotels, I got a call the next day asking me how many people would be in the room, then I received a quote by email the next day with all 4 hotels... except they got the dates wrong (quotes were for 5 nights instead of 4 nights, starting a day earlier than what I requested). Also they quoted me the refundable rate, which I didn't care about, but I did notice their prices matched what was on the hotel website for my preferred option (a Hilton property) so I called them anyway asking to book.
The CWT agent couldn't see the advance purchase rate in her system. She asked me if I was a AAA member but I'm not, so she went on the Hilton website to check the rate. When she saw the advance purchase rate she agreed to book at this price, so I went ahead with the reservation. FYI she did ask me for my HHonors number.
I usually don't stay at very expensive hotels yet after only two bookings I've already saved ~$300 compared to the cheapest rate I could find online. I'm starting to love this card much more than I anticipated.