I put a persistent nav bar at the top of my latest site (http://bosscheck.me) so that potential customers are always looking at a "book now" option. Shallow and obvious, perhaps, but my assumption is that this is optimal for conversion.
Your navbar is much nicer and less intrusive though, I like it. Have you thought about differentiating the booking button from the rest of your navbar elements?
Yes, I've thought about that exact idea probably more than it deserves, but I'm trying to err on the side of not appearing spammy while simultaneously keeping the "book now" button always in easy reach.
