try this site :
http://www.betdaq.com/UI/Default.aspx
as an example go to masters betting on menu ( can't provide direct link )
you can see betting in running & can either "back" bets ( acting as "punter" ) or you can "lay" ( acting as the "bookie" )
as an example,at this instant, someone "layed" a bet on lefty for £485 ( ~ $960 ) at 5.1
tha means if lefty wins on sunday, then that guy will have to pay out
~ 5.1 * 960 = $4896
he can off course "hedge" this later today/tomorrow, if lefty messes up & say drifts to 10/1
then he may actually "back" lefty with ~$490 , at 10/1, so he woud equalise any potential loss from "laying" lefty before
of course, if he's drifted out to 10/1, he's not likely to win so your overall profit is
960 ( from laying ) - 490 ( from backing later ) =
$480
this type of betting is what most serious gamblers in europe do ( unfortunately not to my tastes as sports are too emotional for me ) & it's a liquid market for such glamour events ( currently ~ $9.3million bet on this event so far on this ecxchange )