19
F# is a perfectly good place to start learning functional languages. If you're worried that F# knowledge won't apply to other functional languages, you shouldn't. F# is a member of the ML family of languages. Microsoft just tweaked it a bit so that it plays well with .NET.
Luca Bolognese gave an amazing presentation on F# at PDC 2008. I would strongly recommend you watch it and decide for yourself whether F# is worth learning.