Question came to mind recently, when I remembered that my grandparents always had separate twin sized beds (in the same room).
No, this is not a recent thing. In the past entire families slept in one bed. See the discussion here: http://www.reddit.com/r/AskHistorians/comments/1p0tmm/in_medieval_europe_people_shared_bed_with_family/
Can you specify a region/culture? Marital practices vary widely across the board, so if you'd like a specific and/or helpful answer, more details would be very useful.
Please, no more family anecdotes or half-remembered apocryphal stories. Remember the rules. As was explained in the excellent recent meta post on "What it means to post a good answer in /r/AskHistorians": If you're choosing to answer a question in /r/AskHistorians, there are three questions you should ask yourself first in turn:
Do I, personally, actually know a lot about the subject at hand?
Am I essentially certain that what I know about it is true?
Am I prepared to go into real detail about this?
Can anyone elaborate on the whole two beds for conservative married couples? The whole "pushing the beds together" thing. Is this just on TV or is it an actual practice
Follow-up question: is the bridal bed of Odysseus and Penelope, apart from the live olive tree bit, representative? Did married couples share one bed in ancient Greece?