Finn,
We went last year and I wrote a full report on it here:
http://www.j2ski.com/ski-chat-forum/posts/list/6855.page
What surprised me (I'd never been ski-ing out of season before) was the way that most things were shut. There was a cafe open at the bottom of the glacier, and the restaurant at the top of the funicular was open, but as far as I could see most of the resort was shut and the free ski bus to the chalet wasn't running. So I was very glad the chalet people were there to deliver and collect us from the glacier.
The only very slight snag with the deal at Tignes is that they only collect and deliver people from Geneva once per day. It's nearly a 3 hour drive from there to Tignes. So, if you're flying from a regional airport you might not get a flight to fit in with this, because it's out of season, and have to stay in a hotel in Geneva, which would considerably put up the total cost of the holiday. There are plenty of flights to Gatwick though.
We had so much fun last year that we're doing it again this October half-term. I just hope the weather is okay and they don't have to shut the glacier because of a blizzard or something.
Ally