Civil Unions in Illinois give rights provided by marriage to same-sex couples, but also to unrelated folks that want same benefits without necessarily being homosexual or even same-sex. Protections to marital property and receipt of maintenance (support for the other spouse, or what used to be called alimony), etc. should apply to parties to a civil union. I say "should" as this law was only passed this month and its interpretation will be up to the courts.
Nevertheless, based upon the statutory language, it appears that civil unions can benefit (or suffer, depending on your viewpoint) from prenuptial agreements, postnuptial agreements, and all dissolution of marriage (divorce) procedures applicable until now to Illinois recognized marriages. For instance, marital property may be protected by a prenuptial agreement. It may be distributed by a Judge upon dissolution of a civil union. Maintenance (what used to be termed, alimony) may be awarded from one partner to the other. The list goes on. In addition, folks in many different situations may benefit from this law. For instance, heterosexual friends (same sex or opposite) that are residing in a retirement home, with no intention of marrying each other can share hospital visitation or decision making rights. Previously, such individuals would be excluded from entering the other person's hospital room if the patient is less than able to fully communicate, even if their relationship was decades long. Now, such individuals can enter into a civil union and upon one of them falling ill, can visit each other in the hospital or make healthcare decisions in the event the other is unable to do so. Very importantly, unlike in marriage, this can all be accomplished without affecting each person's pension or social security. This is a "new day" for Illinois indeed. It will be years before we understand the repercussions. Overall, the law seems very beneficial as it offers more avenues of protecting intimate relations between adults. Feel free to read the law's full text: http://www.ilga.gov/legislation/publicacts/fulltext.asp?Name=096-1513.