I thought I might lower the tone a little bit with someplumpes denken, some anecdotalism, from an artist POV.

I wanted to contribute something to the discussion sooner rather than 
later as Jeremy was kind enough to ask me in the first place and though 
I'd maybe like to say something principled and positional later - later,
 since I want to make sure I get it entirely to my liking before posting
 - for the moment I'll confine myself to a few words about my own work 
since it exemplifies some things about possible relationship between 
artists and the work previously made, enabled, realised, sketched out, 
started, 'stolen', 'borrowed', abandoned, envisioned or completed by 
others.
I'm avoiding framing the thing in 
terms of copyright/IP because they are concepts which are not only grey ( in the sense of dull, not ambiguous) but filled to the brim with the 
kind of corporate meaness of spirit responsible for so many current ills way beyond those of artists...

I've always made my digital work freely available. I toyed with the idea
 of formally licensing it under the splendid WTFPL license

http://sam.zoy.org/wtfpl/

but couldn't really be arsed even to do that.
In "Current" the show in which I recently took part at the Harris Museum ( a show about the acquisition & collection of digital art, 
especially by public institutions) I suggested from the start my entire 
piece should be freely downloadable from the project web site by anyone 
-probably far fewer than I'd have liked - so inclined.

I should add that any money I've made from the practice of art has been 
from teaching or from the rapidly shrinking field of outreach/education 
work.

I do feel strongly about putting my money where my mouth is, but it's 
not that I'm asking for applause for my virtue -more that I realised two
 things that are utterly central to me as a human being and artist.
One is that, having worried for a long time about originality, it hit me that forgetting about being original and acknowledging making art as a 
social activity, entirely dependent on a huge chain of influence by, 
borrowing from, insight of those who had preceded me, was the key to 
unlocking in myself the ability to make things that were half way 
worthwhile.
The second was that, in so far as my individual personality laid its 
mark upon anything I made, I was by temperament and ability a 
consolidator with an classicizing impulse. Concretely, when the Warhols,
 Shermans, Calles, Cornells, Framptons, Richters, Naumans & many 
more did all sorts of interesting and in a sense "new" ( though see my 
point one, of course) things, my instincts were to take those things and
 turn them to somewhat conservative (with, naturally, a small "c") 
expressive ends.
So borrowing, appropriating, re-mixing seem to me like breathing - 
natural, necessary and invigorating. It's not a matter of principal for 
me to break copyright law but I couldn't imagine feeling a shred of 
remorse for so doing - indeed I so viscerally loathe the world of 
capital and its excrescences - marketing, MBAs, entrepreneurialism as a 
value to live by, not to mention poverty and war, that anything, however
 minor, which gets up its collective nose can only be welcome.

To finish here are links to two projects. The first is a kind of career 
suicide - I've been obsessively taking still images since last November 
and posting them to Flickr ( a place magisterially reviled by James 
Elkins in a passage in his recent interesting, though somewhat odd and 
unpleasant, book on photography). The link is specifically to a set of 
recent pieces where I've started remixing -and I use the word very 
advisedly- advertising pages from either the Tate house organ, "Tate 
&c".or from the Guardian "Weekend" colour supplement .
The other is to a kind of performative sound art project. Under an 
assumed identity, DJ Mickiewicz, fictionally resident in my late 
father's home village of Miesatycze, Belarus. I'm entering a remix 
competition , once a month. Here's the little blurb for the project:

I’m going to enter a remix competition every month, from Aug 2011 to Aug 2012.
I’m 54 years old and although I’m 
musically reasonably deft I know little about the culture in which I’m 
attempting to intervene.
I know none of the specialised 
vocabulary, can’t distinguish genres and although I understand what is 
being said, just about, I don’t speak the language in which posts or 
comments on this kind of work are framed.
Each of my remixes will be posted here, with a link back to the original track.
My nom de remix is mickiewicz.
cheers
michael

Finally an observation - I started using samples from the (as it 
happens, public domain) Conet project ( audio recordings of "numbers 
stations" originating allegedly with spies of one stripe or another) 
some years ago.
http://www.archive.org/details/ird059
Two of the remix pieces below incorporate such material and it's appeared regularly on the soundtracks of my moving image work.

It occured to me I think of this material exactly as I would my piano, 
or a favourite set of pastels - I reach for it almost as extension of 
myself, my voice or my thoughts. When I use it it allows me to 
expressively reconfigure something very dark, but this use engenders a 
complex of meanings - what it was historically; its great, purely 
formal, beauty; the meaning I add in my re-use and re-contextualising, 
and the meaning anyone who views or hears, or who will view or hear my 
work, brings to it.
I think this richness is something worth considering, valuing and defending.

http://www.flickr.com/photos/szpako/sets/72157627815151006/
http://www.michaelszpakowski.org/mickiewicz/