We spent 5 nights at the Mercer for New Eve. We originally booked a Mercer room but have been upgraded to a Deluxe Studio. The room was fairly big for NYC (i would say 40m2) with a very good bed, high ceiling and a nice bathroom. The style of the room is slightly cold but i guess it is a question of taste. House keeping and bell service are very good.
The big plus of the Mercer is its location, in the middle of Soho and there is very little alternatives in terms of high end hotels. This probably explains why they charge such high prices, although service does not follow:

- there is no concierge. We asked some ideas for gospel in Harlem and the front desk lady made a basic google search and printed the first page for us. Quite frustrating for a 5 star hotel

- we ordered breakfast in room once. The pastries were not fresh and one plate was...dirty. Not really acceptable when you charge 600 usd per night

- there is no spa and no fitness center (you are given a pass to the Equinox around the corner)

To summarise, this is an overpriced hotel and there are probably much better alternatives if you are prepared to walk a little bit.

My family stayed here for the second time in May '11 and booked adjoining rooms on the second floor. It's a fun place, great for celeb-spotting (Karl Lagerfeld this time, Sean Penn and Courtney Love last time we came), and the location is great in the heart of SoHo, but we noticed a few signs of wear in our room: a large stain (coffee?) on the bed base, the leather seating under the window looks worn, and the whole room just felt tired. I asked for a discount as a returning visitor but was refused, unlike 60 Thompson around the corner which gave a generous discount. Also we were disappointed not to be allowed breakfast in the upstairs Mercer Kitchen because an ad was being filmed. Fun but faded.

Very nice rooms with nice little extras. The Swedish schampo was à nice touch. Candy from Dean&Deluca in the minibar was extremly good.

The Mercer is without doubt hip, however, for the price I would have expected better. The rooms are fun, the bathrooms very, very cool. I was a little upset to have deliberately booked a room with a bath-tub (the big ones for sharing).. and got a shower instead. The staff were a bit put out when I asked to move, but being typically British we stayed put. The lobby is beautiful and very relaxing, a great escape from the bustle of the village.

Do not miss the Mercer Kitchen though, this was the best thing about being a hotel guest... a direct lift directly into the restaurant.... food to die for!