By switching to the top 500 address list there are a number of wallets with no activity since 2010 and 2011. The probability that these are LOST addresses is high as is the value.
Anyone want to work out the % of coins involved?

That is disturbing.
I noticed one BTC wallet, which is not active ever since 2009! (198aMn6ZYAczwrE5NvNTUMyJ5qkfy4g3Hi)
This is the number of BTCs trapped in the top 500 wallets, by the year of last activity:
Year 2009: 1 wallet & 8,000 BTC
Year 2010: 10 wallets & 47,466.93 BTC
Year 2011: 104 wallets & 408,009.50 BTC
All together, 115 wallets with 463,476.43 BTC in them.