This question always generates lots of responses and I always find the different responses interesting and informative.
To set the stage, I (1) dislike staying off property, (2) prefer the luxury resorts, but settle for moderates and economy when necessary, (3) like to visit as often as possible but at least once a year, and (4) was looking for accomodations that were more like a condo, as in I wanted more room.
I prefer to breaking the cost down on a per point basis (as someone above suggested) that enables me to compare the cost of DVC to the cost of staying any property of my choosing. Some people spend a great deal of time and energy as they look at cost but I pretty much followed the approach Crisi & Michelemouse use. If you don't want to get into too much precision $6.00 per point seems like a good place to start.
But, cost wasn't the only factor. I can get a nicer, more spacious room for less than I would pay for a less spacious room and I have more amenities. I get to go to WDW more often--two to three times a year depending on what time of year. There is flexibility in terms of locations and accomodations (studio, 1 bdrm, 2bdr, grand villas at some locations, two off site beach properties, and more).
I have no regrets, we could have purchased sooner but we needed more convincing and more time to mull over buying. Once we recognized that we really liked WDW and wanted to go at least once a year---then the decision was easy.
Good luck and pay close attention to all responses. It's still a pretty big financial decision and should not be made lightly.