I've worked from home for about 15 years and love it. For one thing it meant I could get a dog, so I have the best sort of company 
But I do have a room dedicated as an office - though in the last couple of years DH also started mostly working from home so he uses it too, and DDs computer is in here too.
It probably helps that I write software and most of my communication always has been by email anyway.
Sometimes if I reach a mental block I quite deliberately go and do some gardening or cooking or walk the dog- often the problem miraculously resolves on returning to my desk so I don't feel guilty. If I was stuck in an office I'd be drinking coffee or wasting a colleagues time instead. SO, don't feel guilty about apparently doing non-work tasks, remember you're letting your subconcious free!
Since DD went to school I dropped to half-time - but because I don't have to waste time in meetings, getting dressed etc I apparently still get as much done as a lot of full timers.
So I don't feel guilty about taking off on a nice day and then doing a bit more either side (two 6 hour days with a day canoeing on coniston in between, whats not to like?)
The only thing that tends to throw me off course is periodic MN binges.
Hope this reassures some of you that it really CAN work well!