I met a very sad chap the other week, walking about where I work. I'd been out looking at the amazing frost, and he commented on it, as you do.
Then it came out (he needed someone to talk to). He'd just lost his partner. He'd not been allowed to make any decisions on her final care (cancer), not been called to the bedside when she was dying, not been allowed to make any decisions on the funeral. He was devastated. Not being married had cost him being with his loved one at the end as he wasn't the next of kin.
I would want to be married if
a) we were buying a house together
Joint tenants: if one dies, the surviving one automatically gets the other share
Tenants-in-common: if one dies, their share goes to whoever it's willed to
If the value of the house is over the Capital Gains Tax threshold (just £10,600) and the couple are unmarried, the survivor will have to pay between 18% and 28% on the value over this.
(average house price between July-Sept 2012 is £249,958, so you'd have to pay between £20,588 and £32,026 to the Govt even if it's willed to you - who wants to do that?)
b) either of us needed medical care - next of kin decisions
c) we had children (preferably before!) - automatic parental rights for Father, if things do go pear-shaped, you're more likely to get support for you as well as them
d) there was any suggestion of any relatives on either side who disagreed or disliked either of us - see b)
e) It's a good excuse for a party.