No experience, but studies have found minimal or no effect in fat burning. I believe the supplement is reviewed and the article referenced on JB's website (www.johnberardi.com).
To provide some insight, mainly because I'm bored, L-Carnitine does not have much effect for the following reason:
In lipolysis (fat breakdown), the fat cells must pass into the mitochondria to provide energy for the person. In passing one of the membranes of the mitochondria, the fatty acyl molecule must be attached to an L-Carnitine molecule via a special enzyme called a "L-Carnitine Acyl Tranferase." Therefore, basically three different molecules play a vital role in the fat burning process, in addition to many hormones. Without going too deep into the subject matter, L-Carnitine is probably not the one molecule that does exists in insufficient amounts, rather the enzyme.
Basically, through analysis, L-Carnitine and Fat are both supplied in sufficient amounts, but the enzyme is probably not. Therefore, if we can somehow trigger the production or activation of the enzyme, we can probably burn more fat.
Just a theory that I thought I'd post.