Here's what I usually do to clone recipes.
First, go to Beeradvocate.com and find your target style. For instance, a Witbier:
Witbier - BeerAdvocate
Then, click on the "View the Top Beers" link near the top of the page:
Top Beers - Witbier - BeerAdvocate
Scroll through the top beers to one you have enjoyed and know you want to clone, or you can use the list to go buy it and try it first.
Next, read the reviews of your target beer. Here, I focused on "St. Bernardus Witbier":
St. Bernardus Witbier - Brouwerij St. Bernardus NV - Watou, Belgium - BeerAdvocate
Next, visit the target beer's website, if one exists, to find the ingredient list. Most awesome beers will have one. Here, St. Bernardus doesn't have much information:
Sint Bernardus
All it really says is that it has a unique secondary fermentation and the recipe was developed by the same dude who made Hoegaarden and Celis White, Piere Celis.
Then, see if anyone else has cloned it for pointers.
At this moment, we know three things:
1) It's a Hoengaerden kin (the apple doesn't fall far from the tree)
2) It has a target ABV of 5.5% alcohol
3) It's a "traditional wheat beer" from Belgium
I haven't found one for this style, but I think Clone Brew or Beer Captured may have it.
Anyway, then you tear the recipe apart in the BrewMasterswarehouse.com BrewBuilder 2.0 and tweak it to match the commercial brewer's ABV, S.G., O.G., IBU, SRM, etc.
Once you have something that matches, tweak it to your personal tastes, and run it by the dudes on the homebrewtalk boards.
If all turns out well, then give it a brew and see what you get!
So, that's what I do... Any thoughts?