Saxis,
If you want a full sized spare for offroading but don't mind a smaller spare for highways, you can get the spare and then just carry it in the trunk (a la Jeep). Or you can carry it in the trunk all the time, but it'll take a lot of space. Old Blazers were like that.
DZP,
Are you serious? the space savers always looked way smaller to me, but the last time I used one was back in 97 or so. And they are rated for only 50MPH, at least ours was (my dad wasn't too happy about driving the remaining 2 hours of the trip doing 50MPH, which of course got extended to 2.5 or so).
I wonder what GM did with the Acadia/Traverse/Outlook/Enclave in terms of spare tires. A friend said that 2010 Escalades come with a fix a flat instead of a spare, which is a really stupid idea. hopefully that got ditched in favour of a real tire.