I've fallen for this a number of times now and assumed it was me that had made the mistake.
But it's not, and I've got screenshots.
I'll do a Google search and naturally if Mumsnet comes up in the top 5 I'll invariably check the date and click through if it's current. The threads are years old though! Today I wanted to know what the Weight Watchers No Count foodlist was and Google told me someone had asked the same question on Mumsnet in Jan this year. I click and discover it was actually from 2005! I've checked the thread and no-one even posted on it in January.
So why is this happening? This must be why so many zombie threads are appearing, people (rightly) think they are active.