If it's less than a second in duration - more a brief flicker than it actually all going black for a second - then I have a similar problem with my MacBook Pro (mid 2009 15" model). It's very sporadic, but it seems to be related to the computer being under heavy load (eg running 2 large virtual machines simultaneously) when it's running on the integrated graphics (in energy saver, using 'better battery life' instead of 'better performance'). I've never had it happen on the 'better performance' graphics setting, and I suspect it's something to do with the low-power graphics card.
I do keep meaning to take it to a Genius bar when I get a chance, because it's still under Applecare and it can be annoying (it tends to happen in a flurry of flickers for a minute or two, then nothing for hours on end). However, it's my main work machine and I'm not in a position where I could be without it for a few days, so.... :-)