There are a number of ways to account for it, and, just like many things in the personal finance arena, up to you. Since it's a number that doesn't matter (net worth) but is just for your own pleasure, pick whatever makes you feel warm and fuzzy.
I personally don't even count my pension (but it'll be pretty small when I finally take it 20-30 years from now, maybe 5-9k annual or so in real dollars).
My favorite two methods though for those that do count it is to either:
1) Take the NPV of the income stream, or
2) Price our a comparable annuity (in this case a deferred annuity) from an insurance company and value it at that (market) price.
I don't favor the "count up the contributions" method, because I don't think it gives you an accurate value. But if you want to do it, it has some advantages (simplicity, for example). Like I said, choose whatever you like. :)