I do - I have a written investment policy for our family as well as a written policy for what I will pay for college (I call that one the College Compact). For anyone looking for a great resource on IPS, I highly recommend checking out the Bogleheads site (link to IPS wiki page here) as well as searching their forums.
Mine is two pages long and covers:
-Stock/bond allocation goals over time
-Large/mid/small cap and short/mid/long term bond allocations
-International fund goal
-Emergency funds-how much to have and where they're to be located
-College savings philosophy summary (the detail is in the other document I mentioned)
-Target annual investment amount
I believe creating one is useful in several ways.
- Creating it helped me to think out my ideal investment strategy in more detail
- I can easily compare this ideal to what I'm actually doing and see if there's a gap-for example, am I under- or over-weight in a certain part of the stock market
- It will be helpful during a downturn to remind me of what I'm doing. Although I've invested through both the 2000 and 2008 stock market crashes so I'm not overly worried about this one, but I know how scary it can get
- In the event that I become disabled or pass away, my family can use it to manage our savings and investments