I found a website while looking for patterns on http://www.ravely.com/ called http://www.myrecycledbags.com/. The website both shows you how to make plarn out of grocery bags - but also give you a million ideas of what to do with it when you're ready! I made this using the pattern on the site roughly - I did the first five rounds as the pattern and then just winged it. Very cool way to recycle the old grocery bags. My only problem is that I have already switched to using the 'green' bags for groceries and I'm going to have to put a call out to everyone I know to collect these for me.
The finished PLARN!! Total of about 50 bags.
The finished bag!