How often do companies seek reimbursement on relocation expsenses?

I just relocated with my company to a different state with all relocation expenses paid for. I signed a contract for one year, stating that if I voluntarily resign or am terminated with cause, I am liable to pay all monies back. Do companies usually seek this money? Does anybody have experience with this? I would have to imagine that a large company wouldn't want to go through the legal aspect and expense of recouping those funds. Any thoughts?