The issue of returning extra coins sent in error isn't as black and white as either side seems to think.

The general principle (in the UK) is that if you know they aren't yours then you have to return them.  Where the problem arises here is that, so far, nefario hasn't released the information necessary for people to establish how many coins they were actually supposed to be sent.  Once he's provided .csv files of transaction histories then people can verify how much they should have received and return the extra.  Right now he hasn't even given a good explanation of why GLBSE had to close down in a rush - let alone given the information necessary for people to verify what funds they were due.

His primary (original) reason for shutting down was AML.  An entirely credible reasons - but undermined by his subsequent behaviour.  He initially insisted that his legal advice was that he had to obtain ID info for everyone - then retreated very quickly from that position without any explanation.  Was his original legal advice wrong?  Was he just making up that legal advice?  Who knows.

It is absolutely 100% certain that he misled or lied to his fellow shareholders in their irc discussion in respect of his legal advice.  There is NO WAY that a single solicitor could represent both GLBSE (collectively) and nefario (individually) when (as was made perfectly plain in the irc log) his personal objectives were definitely not fully aligned with those of all his fellow shareholders/officers (the officers is the key part).  There's also NO WAY a solicitor could give advice to the company as a whole whilst telling nefario he couldn't tell his fellow officers about it - if the information was only relevant to nefario then his PERSONAL solicitor should be dealing with it.  It's also standard practice in the UK that when advised by a solicitor on a significant business issue, you are then sent a written summary of their advice.  This should have been provided to (at least) the other officers, if not to all shareholders (there's a difference between passive shareholders and actual officers who participate in running the business).

I can understand nefario maybe not understanding what a conflict of interest is.  But I'd be shocked if a solicitor didn't - they tend to try desperately to avoid such conflicts as it leaves them open to liability and complaints of malpractice.  I've had a solicitor refuse to advise me on an issue that arose whilst I was working under instructions from them (and a barrister I was working with on the same matter also refused to give advice) even though the actual solution to the issue that had arisen (which was arrived at after taking independent legal advice) was fairly simple and not detrimental to any of us.  I can only surmise that nefario either consulted on an individual basis and/or played down the involvement of theymos etc such that the solicitor concluded they had no part in actually running GLBSE.

In short, nefario has been less than honest and open so far - both to users of GLBSE and to his own business partners.  There's, thus, no reason anyone should be willing to take his unsupported word on what they're owed.  And how much should be sent back anyway?  Has he even ever stated whether the whole 2nd payment was an error - or was it meant to be sending the last 10%?

Note: I received all (I believe - though can't confirm obviously) my tiny amount of funds back in the first batch of payments.  I haven't received any 2nd payment so have nothing personally to decide whether to return, how much to return or who to return it to.  If I HAD received an overpayment then I'd be putting the 2nd payment in cold storage then waiting until I had the information necessary to determine precisely what I WAS owed AND had either received back control of my assets OR received a good explanation of why they weren't being returned before sending any funds anywhere.

If he's spewing funds around at random then there's no guarantee returning them to him would get them to whoever their rightful owner is anyway.  He could have just disabled trading/transfers and left the site up so we could withdraw and verify our holdings now that he no longer required ID information.  And if there's specific accounts that he can't do that on (e.g. if he has been given specific instructions in respect of asset issuers) then the withdrawal functionality could have been removed from them.