If the spouses have not kept their non-marital property separate, but they have combined their ownership in joint tenancies and otherwise, how does the court decide on property division?

Non-marital property that is placed into some form of joint ownership is "commingled property". Unless otherwise agreed by the spouses, commingled property is treated as follows: (1) When marital and non-marital property are commingled by a spouse contributing non-marital property to the marital estate, or by the parties contributing marital property to a spouse's non-marital estate, resulting in a loss of identity of the contributed property, the contributed property is transmuted to the estate receiving the contribution. Example: the wife contributes inherited (non-marital) funds to the purchase of house which is held in joint tenancy by both parties. The wife's non-marital funds are transmuted to marital funds. However, (2) When one estate of property makes a contribution to another estate of property, or when a spouse contributes personal effort to non-marital property, the contributing estate shall be reimbursed from the estate receiving the contribution notwithstanding any transmutation. Reimbursement can only occur with respect to a contribution which is retractable by clear and convincing evidence, or was a gift, or, in the case of a contribution of personal effort of a spouse to non-marital property, unless the effort is significant and results in substantial appreciation of the non-marital property. Personal effort of a spouse is considered to be a contribution by the marital estate. The court may provide for reimbursement out of the marital property to be divided or by imposing a lien against the non-marital property which received the contribution.