I started as a guitarist and two albums spent more time on my turntable than any others- "The History Of Eric Clapton" and "The Duane Allman Anthology". Duane's playing was a huge revelation to what slide could sound like. I like Elmore James et. al., but Duane's smooth and very precise sound opened up a whole new realm of expression. I suppose that's partly why I love playing fretless too. Big influence as for how slide should sound to me are Duane (and his psychic protege successor, Derek Trucks), Bonnie Raitt (and her original long-time bassist, Freebo, was a bigger influence on my fretless bass approach than Jaco or Percy), Sonny Landreth (how does he THINK of all that stuff!?!?), and Lowell George.
I don't have any of my guitars set up specifically for slide, and so I seldom play in open tunings any more. I like the action on the guitars a bit higher than most guitarists do anyway, and with a light touch and real Coricidin bottle, using 10's or 11's works just fine.
John