The only time I've been burned by my contract is from relocation expenses. I went to a company to take a job and not long into it a reorg moved me to a different team. I left the company and they demanded I pay back my relocation expenses. When I protested that they changed my role to something not what I was expecting, I was told that according to my contract it doesn't matter. The temporary housing I was put in was very expensive despite the fact I hated it. Luckily, my balance was paid as part of a signing bonus by my new company.

My lesson here was: Never take a relocation package that has the company sorting your housing and travel, just ask for a large signing bonus instead.