That 1% is a lot in my opinion, taking into consideration this is just a corner of the glacier, I guess there maybe in total 5% lost..
I wouldn't be surprised if it is more like 2M BTC lost. In the first year+ of Bitcoin's existence (during which almost 2M coins were mined) it was nothing more than an interesting experiment. The coins were worthless, and people treated them as such. I mean heck, the first known monetary valuation wasn't until Lazlo's pizza, which was mid-2010, 1 and a half years after it started. Not to mention than Satoshi himself mined a good 1M BTC, and I don't expect those will ever move.
Just my best guess on it. I'd be willing to bet that 10 years from now, there will be at least 2M coins that haven't moved between now and then.
I believe that bitcoin was actually trading on gox prior to Lazio's pizza purchase; this transaction was only the first known transaction that both involved bitcion and actual goods/services.
I do agree with that that in Bitcoin's early days, many people likely treated their private keys with little care. I would not however underestimate the potential for technology to be able to recover data once it has been seen by either the human eye and/or has previously been stored on a hard drive
If you do a forum search for "mtgox" with a message age between 1640 days (how many days it has been since laszlo's first post) and 9999 days, only one post comes up, and that's only because it was edited a year later. So no, I do not believe MtGox was trading before laszlo's post. Surely there would be announcements and chat about it on the forum if it was.