Only if you plan on dying, most people don't. They just get a large bill when a loved one dies. I can't remember the details but it was reported a while ago that siblings who lived together in london got royally fucked over when one of them died and the house was over the tax threshold (this was back when it was raised to 325k).
I think the trusts are normally set up by the really rich. The goverment extending the time for giving gifts from 5 years to 7 years (before death) a while back in an effort to make it more awkward to get around the rules. The same was putting restrictions on farmland (which was exempt inheritance tax)
I sure you can't just write your spouse out of the will. (I seem to recall it was changed because some people left it all to the dogs home and the spouse discovered the joys of living on the street).
Most people are exempt the tax anyway, but some are kicked in the nuts because of it. As well as siblings, there are other relatives living with an family member other than a spouse who might have a ton of money tied up in the house but no other assets only to find they must sell the house if that family member dies. There are also family run businesses which can be hit with a hefty tax bill if the mian family member dies.