Does anyone ride BMX? Are the skills needed/learnt on a BMX transferable to a mountain bike? I'm thinking that in those odd 30 minutes with nothing to do moments I could just tuck the leg of my jeans into my socks and have a quick play on the street outside my house possibly graduating onto the skate ramp on the park. Will this playing improve my general mountain bike riding skills? Will I just look ridiculous?

If anybody has BMX experience what would they recommend as a starter bike? I'm hoping the tiny wheels will mean I could sneak it into my collection un-noticed!  

Yeah, go for it - tiny wheels are great and all that extra weight and lack of gears does wonders for fitness .  Who cares what you look like? - can't look any more ridiculous than me at 50 years of age still dragging the little ramps out of the garage for a play in the street - my kids have grown up and moved on . . . me? . . . no chance .

Have a look at Custom Riders - http://www.customriders.com/prodlist.asp?a=specialoffers&cat=1010&parent=9999&sid=3&sort=3 (that Volume Black Sheet looks a cracking buy) or Alans BMX - http://www.alansbmx.com/index.php?cPath=21&osCsid=9814c4ec653432443ee37a8f97b06c17.  Both recommended shops with great service and advice.  Try to look for tubular 3 piece cranks and 36 spoke wheels to save a little weight (solid cranks weigh a ton).

Here's mine, built up in a Y2K non-anorexic stylee in an effort to recapture my forties  - it's great! . . . oh and check out http://www.wofbmx.com/

Am sure all that fancy stuff must help with bike handling skills etc.

Don't know entirely about mtb after that but look at Shanaz Reade and Jamie Staff the quick starts of bmx are transferable to track sprinting.