There are some possible reasons why he is sharing it with this forum:
1. He did not know about wallet cracking services. Though a quick google would have shown it up.
2. He don't trust the wallet cracking services and wants it out in the open.
3. He wants to see if anybody has the computational horse power to crack these passwords to verify how safe bitcoin actually is.
4. Most likely the wallet.dat is stolen and it is therefore too risky to send it to a wallet cracking service, this way he is hoping to catch some of the money for the cracking work of others.
Whatever the case may be my advise to whoever cracks it if real is to do the following:
1. Keep 3.0 BTC for yourself.
2. Send 0.5 BTC to him.
3. Show screenshots that 0.5 BTC was send to him.
Step 3 is very important, because this builds some level of trust and word of mouth that forum-ites on this forum can actually help and re-gain funds. This may bring in more oppertunities for forum-ites.
So at first glance sending 0.5 BTC to him seems sour, but it could be a very smart thing to do long term.
Anyway finally if the original poster does receive some BTC he also be smart to post it here with some screenshot for the exact same reaosn as 3. LOL.
GOOD LUCK.
(P.S.: The last time I investigate such an offering, it was in a different way, it was real... so....)
*addition*:
One remaining and intrigueing question remains:
Suppose it's number 4. The wallet was/is stolen, then how does the poster know that the password is 8 characters long and numbers and letters ? This would imply that somebody observed somebody else typing in the password and may have seen the number of fingers being used or key pressed being made. It could also be the number of clicks on the keyboard.
This could also explain why the estimate is not exact but somewhere between 6 and 8. (If you do try I would recommend going up to 9, if feasible/possible !
)