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.
Thats 12M divided by .463476= 5.5617% of bitcoin potentially dead in lost wallet addresses. Now add .5% a year (average loss of currency through death (sudden or otherwise) NOT including lost wallet addresses for other reasons and in 20 yrs from today 15% of bitcoins lost 40yrs 25% + 80 yrs 45% + approx. Here is one of bitcoins major flaws.. NO method of identifying and replacing lost coins which is unstable and potentially inflationary.
Revised % is actually 3.8% ...... 12M divided by 463476 = 25.9..100 divided by 25.9 = 3.8% slightly lower but the principal is the same and does not count any losses from the other 11M wallets not in the Top 500 against the same number of coins.