If your landlord manages to break your rent-stabilized tenancy by claiming the apartment for his or her personal use, or the use of a family member, the law requires that "use" to last for at least three years. If a Court awards the apartment to the landlord, and it isn't occupied for personal use for at least that length of time, penalties can be imposed on the landlord. Note that if you make a deal with the landlord and agree to leave in exchange for certain benefits, you may forfeit the opportunity to bring this suit within the three-year window. The landlord must obtain a judgment against you without your consent, forcing you to leave, in order to for you to retain that right. So if you are thrown out, stay friendly with the neighbors or doormen, and check in with them once in a while to see what's going on.
Attention New York City Tenants: Get more information on personal use suits at the McAdams Law main site here.