Somehow I doubt that these guys have the drive and sticktuitiveness to go after the OP in court. Seems that they're either too shy or too lazy to even talk to potential customers, much less fight you in court for another idea that they wouldn't follow through on anyway.

OP should probably take sensible precautions like saving all his e-mails (off of company machines!) and staying on friendly terms with other employees who might one day be called as witnesses. But I wouldn't recommend "ragequitting", just go politely.