I booked accommodation with this site: http://www.svalbard.net/?set_lang=en
I then booked my activities on the spot. Bear in mind that some activities are not available every day before you book your accommodation.
I was at Guesthouse 102, which is where the polar bear came down from the glacier last June and sniffed around (must be a rare event, as I was told the last human fatality from a bear encounter on Svalbard was 15 years earlier - on the hill opposite the hotel). You share, but only with 3 other people and it's a great way to meet other travellers. There are enough showers and other facilities that I never had to wait.
Best of all, it's inexpensive. The only drawback is that it's a 10-minute walk from the centre of the settlement, and the return walk is uphill. Even before the polar bear incident I felt a little uneasy on the uninhabited stretch. On the plus side, I was able to get up close to a local reindeer and get some good piccies.

I was at Guesthouse 102, which is where the polar bear came down from the glacier last June and sniffed around (must be a rare event, as I was told the last human fatality from a bear encounter on Svalbard was 15 years earlier - on the hill opposite the hotel).
An indication of the infrequency of polar bears in the vicinity of Longyearbyen, at least in summer, is the operation of a campsite without fence or armed guards. Their website contains lots of interesting info for budget tourists, even if you are not quite that low budget. http://www.longyearbyen-camping.com/ A colleague of mine stayed there.