Stayed there 4 nights with my wife, we arrived early in Bangkok, check in supposed to be at2pm but we were there around 9am, it took them 45min to prepare the room and we checked in that early without extra charge or single comment from hotel staff (some other hotels tell u off if u arrive that early!!), reception has a tropical atmosphere with trees and water running around which was nice,
Hotel staff :extremely polite-smiley and very helpful,
Rooms: as any 5 star hotel, with a Thai decoration, seperate shower-bath
Location: great location in central bangkok, close to all shopping centres, next to sky train station (chit lom),walking distance to silom park-MBK-Siam paragon etc
Breakfast: variety to choose, starts 6:30am
Tours: they do organise privite tours, our guide was there within 15 minutes!! reasonable prices (floating market- siam niramit, etc..)
View: from our room (12th floor) we could see silom park

1 thing i did not like: you have to pay to access internet from your room,i coul pick the signal up but u need to register and pay to use it which was bit odd for a 5 star hotel, there is a computer room in the lobby but again u gotta pay to use it

overall: if you could afford it then go for it, u wont regret it.

I stayed at the GH Erawan for 5 days as part of a conference that was held there.

I found the stay to be excellent and up to the Hyatts group standards. Some of the points to note are:

Location:

45 minutes from the airport and connected via an overhead walkway to the BTS skytrain station. The same walkway takes you to a number of shopping mall i.e. Amarin plaza, gaysorn plaza, central world etc etc without you ever needing to get down to the street level. As other posters have mentioned, the skytrain will take you to other closer destinations like siam center, MBK etc.

Business:

I agree with a previous poster, the business facilities are amazing. "The Residence" is gorgeous and the meeting rooms could be mistaken for the plush sitting rooms / drawing rooms in a mansion. There is a large kitchen where we had a team building cook out session. This place is in addition to the standard meeting rooms and halls in any addition. Highly recommended for business meetings.

Customer Service etc:

Typical Thai attention to customer service. Requests promptly handled with courtesy. The breakfast buffet is large but was not to my taste as the variety was more focused towards oriental delicacies and pork dishes. Room service food is pretty good however a tad bit expensive (considering the fact that you are in Thailand).

All in all, this is a classy place to stay in Bangkok and highly recommended.

Loved this hotel. Staff are friendly and nothing is too much trouble. Stayed for almost 2 weeks for work. Meals were always of an excellent standard. The Spa is outstanding, Would recommend anyone to stay here,

The stay in Grand Hyatt Bangkok is fantastic. From the arrival to hotel , the receptionts bring me all the way to the check in counter. After check in, they also take me to the room and show me all the function of the button, washroom facilities and even give me maps and directions in my hotel room. The concierge desk service is excellent. The award spa is the best in Bangkok.
The most important is the customer service is excellent. When you are looking for something, they always offer to help and smile.