I often use Booking.com when I book hotels all around the world. I have booked hotels in China, Thailand, Portugal, UK, Sweden, Norway, Croatia and so on. And it works very well. Most of the times. With Oslo as an exception. The two times I have booked via Booking.com in Oslo there have been problems. Who's to blame? Probably the Oslo hotels. The problem is that the Booking.com site does not allow you to make a review of hotels you have not lived in, and hence people do not get warned. And Booking.com is, after all, a site that is dependant on its customers' reviews.
In August 2009 we were going to a wedding. The reception was in Grünerlökka so we booked the Anker Hostel. We arrived in the evening and the rain was pouring down. At the reception I was told that we had been relocated to another establishment, the Anker Hotel, next door. That turned out to be a better option so we had no reason to complain. Only that it had been nice to have been told in advance. When giving the usual review I did not get the option of ticking 'was relocated by hotel', all options are focused on that you did not stay in the hotel by your own choice.
This summer we were having friends over from the UK. We were to meet in Oslo and I booked an apartment in Chateau Apartments in Grünerlökka. I even emailed them to make sure it was OK that we stayed two couples and one 3-year old in this two bedroom apartment. The booking took place in the beginning of May. When we arrived in the middle of June it was raining cats and dogs again. Driving into Oslo our friends call us and tell that there is no apartment for us in the hotel. Instead they have relocated us to another hotel close to Frogner, in a completely different part of town. They claim to have emailed me but this is simply not true since all other emails from Booking.com reach us but not this one.
Upon arrival to the new hotel we find that Chateau Apartments has booked us a double room with two extra camping beds. That we were to share, four adults and one child. They thought that this double room was an OK replacement to a two bedroom flat with kitchen and livingroom area. We didn't think so and thank's to the new hotel and their good relations with Booking.com we got two double rooms. It worked OK but we missed out on the evenings together, after the child had been put to bed. And we missed out on Grünerlökka.
So, be careful should you decide to go to Oslo and book via Booking.com. This warning only has to do with this particular city. As I wrote above we have had no problems booking rooms in Beijing, Bangkok, Oporto and other places, probably because we have happened to choose serious hotels.
Booking.com offered to reimburse us for any extra costs. We didn't have any after having to argue for a while in the new hotel and after the manager came and settled everything. Probably after having had a discussion with Booking.com. So this critique mainly refers to the Chateau Apartments.