[susan53]

You've used while incorrectly. It's a subordinating conjunction like although and not a co-ordinating conjunction like but. So there must be a main clause attached :

We rarely eat oranges in the summer months. While/Although they cost hardly anything from November to April because they're locally grown, the price rises steeply between May and October, when they have to be imported.

While/Although history is really my favourite subject, I know that as a degree it wouldn't be much use for getting a job.

In style, it's neutral. But as I said before, co-ordination is much more common in spoken English than subordination, so it is rarer in spoken English. But because of the subordination, not because of the word itself. When it does occur, it therefore tends to occur in situations where the speaker is taking a long turn (speeches, radio interviews etc) rather than in social conversation. Here's an example :

While I sympathize with the caller from West Calder, I feel we pay poll tax as well to cover all these things...