My brother and neighbor constantly bring this up in discussion when we talk about fuel prices. Sounds like a great idea but I'd be cautious about getting 'free' oil. I'd try a few places local to you to make sure you can in fact get free oil.
I had a 2001 VW Jetta TDI that I sold to get my Dodge. Although I had issues with the Dodge I still won't sell it for a high mileage VW. The pickup just my live style perfectly dispite my 72 mile commute to work. So I am seriously considering this.
If anybody has experience with this, even if not for the Dodge, I'm interested to hear you thought! Oo.