I love clouds. As you may have noticed from my 'Clouds and Sky' Flickr set
And there's a book! The Cloudspotter's Guide!
*adds to wishlist*
 I love this sort of thing - people who are so passionate about their 'thing' that their enthusiasm just sparkles off the screen. Gavin Pretor-Pinney is just such a bloke, delightfully eccentric and boundlessly excited.
I used to look for that in interviews - find the button which gets the candidate all enthused, and see if it fits what we were looking for.