I separate work and personal primarily because I use a Palm and my workplace doesn't allow me to use it in conjunction with my work computer (can you believe that?!?!).
I have found that I actually prefer keeping work and personal separate; I see them as my 2 primary contexts, with @Calls, @computer, etc as subcontexts for each. This works well for me because the separation makes my NAs more manageable and easier to track & I don't do personal things at work. Any work items I think of at home I put into a @Work context and these items get input into my work N/As. If I have work items I want to review at home, I put them on my Palm as NAs and on my work list as @Home.
Anything done outside the office is on my Palm, including things I must pick up for work. For example, my Palm has 3 @Out subcategories which prefix every @Out NA--"H"=anything related to Home; "O"= Out (anything not requiring something from hme or work; "W"= anything related to Work. For example, if I need file folders for work, I would put: "O: buy file folders." Once purchased, if I was not on my way to work, I would add the NA: "W: take file folders to work." This works for me because I've gotten into the habit of looking at my @Out category whenever I to somewhere.