Stayed at hotel Arena for three nights during a business trip to Amsterdam. The hotel is a little outside the city center, but this is no problem with the good public transport available in Amsterdam.
The staff in the hotel was friendly and helpful, and the rooms was very nice and stylish. I had a standard deluxe room, and both the room and bathroom was clean. The only minor complaint I have about the room is that the windows was facing towards the entrance to the hotel, where the hotels night-club is located, which was making some noise. The breakfast at the hotel was good, however the staff working in the restaurant was sometimes slow to take orders.
The only negative about my stay was the so called "high-speed internet connection" (wired) costs 15 euro per day, this was a complete rip-off. The connection was very slow, and sometimes it did not work. Wireless internet was only available in the lobby, and costs 12 euro. In 2010 internet access at hotels should be free!!