artists_beware | Need Advice - Long Wait for Commission (Reply)

I find myself in a delicate position with an artist I commissioned some time ago to produce a piece for me and I was hoping this community would be able to give me some advice on how to proceed.

I do not, at this stage, want to reveal the name of the artist in question. They have been very friendly and pleasant at a professional level and I don't want to tarnish their name or anything, I just want some ideas about how to communicate with them more effectively.

Here's a basic summary of the situation.

26/01/2011 - After discussions of what I wanted and what they were able to produce the (at this stage very enthusiastic)the artist confirmed via email that my commission was slotted for the two weeks between June 6 and June 17 ("give or take". Later that day they confirmed that they had received my payment of $300, a 50% deposit for the piece (a significant sum of money, in my opinion, but something I was and am certainly willing to pay for the piece)

15/05/2011 - The artist sent an email explaining that, as a result of personal circumstances, they would be rescheduling and that "The latest I would start your (piece)... under this new schedule, would be mid July, and it would be finished and in the mail before August."

19/07/2011 - Sent out a bulk email to commission clients "...you may need to wait longer than expected for your product".

1/11/2011 - The artist sent a note on an art website stating that had made some but not all of the components for my piece but that they had not taken photos yet.

1/01/2012 - The artist sent out a bulk note to all commissioners on an art site stating that they intended to have all work completed before they left for FC.

18/01/2012 - The artist posted photos of the parts they had completed for my commission. It was still not entirely complete.

This is the last time I have spoken to or heard from the artist and I am unsure of how to proceed from here. I am concerned that if I push too much they may not complete my commission at all, and after waiting so long I really don't want to give up now (especially when I have already paid a $300 deposit!). What would be a polite and non-confrontational way to ask this artist what the progress of my piece is and when I can expect it to be completed? How much longer do you all think it is reasonable to wait without being given a deadline.

Oh, and in case it makes a difference to your opinions on what I should do, I do know for certain that the artist is currently producing other work.

I try to be as patient as possible with artists I commission and I really don't want to be a bitch or anything. I just need to know when would be an appropriate time to contact this person without being unreasonable and hassling them and what exactly I should be asking them for (a concrete deadline? more frequent contact? a refund?)

Please help!