I have employed it with good results, as far as I can tell.
Here's the pedigree of a 2yo colt I bred.
http://www.pedigreequery.com/handsomeness2
He is level-headed (darn right sweet!) good boned and very correct. 16 hands and built like his breeding indicates. He wont race until he's three.
Have several other young horses bred on the same principle. All of them are big, correct and even tempered too.
When I inbreed I am careful about the types I use. If using Storm Cat I will only breed correct and good tempered stock. No use in inviting disaster.
Here's the pedigree of a very fast colt who is inbred 3 x 3 Storm Cat. He's earned almost $1 million:
http://www.pedigreequery.com/bridgetown6