Thought I would post some details of my recent Tromso trip here to try and help anyone thinking of going.
Tromso centre itself is a hodge-potch of old-style wooden Scandinavian houses (attractive), newer more functional blocks (not attractive), and a few gems such as the library (modern, but stylish) and the old wooden cathedral. The main shopping street (Storgata) is part-pedestrianised and contains most of the shops you'll need.
I stayed at the Rica Ishavshotel on the quayside - nowhere was more than a 5 minute walk away and the hotel was excellent with buffet breakfast included. My room had a great view out over the fjord with the Arctic Cathedral in the background. Getting there from the airport was easy - the SAS Airbussen takes 15 minutes and stopped right outside - 55kr each way.
First stop for any visitor should be the tourist office - incredibly helpful and able to book all manner of excursions and trips. For those - including me - who hadn't learnt any Norwegian in advance you'll be pleased to hear that English is universally spoken.
In the town I visited Polaria (a 10 minute walk just past the Mack brewery) which features a seal pool and other aquatic displays (similar to the Sea-Life Centres) and widescreen films about Antarctica and, more relevantly, Svalbard. Good for children but a bit lightweight for adults.
The Polarmuseet on the quayside is excellent and well worth visiting with lots of interesting displays regarding the tradition of hunting and trapping and telling the story of polar explorers such as Amundsen.
The Perspektivet Museum on Storgata is mainly photography-based but again is very interesting, particularly the collection of old Tromso pictures.
Finally the University Museum (10 minutes on bus route 37) contains a number of displays, although little of the information here is translated into English. The interactive "make your own Northern Lights" display was out of order, but the exhibition of Saami culture was worth seeing.
The Arctic Cathedral was unfortunately closed for renovations and the wooden Lutheran Cathedral was shut too (even though according to the tourist leaflets it should have been open).
As for excursions I had booked a trip in advance with the photographer Kjetil Skogli (he of the Joanna Lumley fame) which was amazing. He did indeed find the Lights after a 2 hour drive (Tromso itself was cloudy that night) and I have a large number of excellent pictures to remember it by. You will need a decent camera, or else Kjetil will hire one to you. He is not the cheapest by a long way but most trips will only take you to one site and if it's cloudy there, unlucky. Kjetil will really put himself out to keep going until he finds the Lights for you and is well worth the expense.
The evening trip to the Wilderness Centre was also well worthwhile with reindeer and a fantastic Lights display (apparently one of the best of the year so far). The guide was helpful, cheery and informative and the Saami hosts happy to answer all questions. To my relief they don't try and pretend to tourists that they still live in tents - as our host said, it's much quicker to round up your reindeer in a 4x4 these days then go back to your house at night to watch TV!
I also had a day dog-sledding at the Lyngsfjord Centre which was an amazing experience - and terrifying at the same time, having never tried before in the most stunning countryside. Well recommended and you'll never meet friendlier dogs!
The weather was much milder than expected (abnormally so) in that there had been no snow in Tromso city for almost 5 weeks. Most of what was left melted over the course of my trip, but on departure day it was coming back down with a vengeance. There was, however, no shortage of snow out in the countryside and particularly away from the coast.
Finally it is true what they say about Norway being expensive. Very, very expensive. Beer is almost £9 a pint and even a can of Coke will set you back £2.50. In a restaurant a simple pizza, garlic bread and soft drink will set you back £30 - £35 each and steak and chips £40.
Despite that, however, I would recommend Tromso and hope to return again.