Tim Ferriss, bestselling author of the excellent book The 4-Hour Workweek and someone who has thought a little bit about the nature of work (and, as he calls it, "lifestyle design"), is apparently a big fan of the generalist mantra. Check out this post at his blog which lists The Top 5 Reasons to Be a Jack of All Trades.
1) It's more fun, in the most serious existential sense.
2) Diversity of intellectual playgrounds breeds confidence instead of fear of the unknown.
3) Boredom is failure.
4) In a world of dogmatic specialists, it's the generalist who ends up running the show.
5) "Jack of all trades, master of none" is an artificial pairing.