Paul,

A couple more comments:

Don't try to get youself up to any speed instantly but work on gradually. I think that its far more important that a tune is expressed properly than being forced out at a pace that the player is clearly struggling with.

I you do go to a session and you want to play a tune. Don't be afraid to start it at a pace that you feel comfortable with even if that may seem a lot slower than the preceding sets. I think you'll find that most players will happily slow down for a couple of sets of tunes to help someone else along (but are unlikely to want to do that all night).

Jon