That sounds fun -- knitting right off the spindle :-)
Usually I'll wash and set the twist in my yarn before knitting, but there's no rule that says you have to. Singles usually have at least a little extra twist. If they are low-twist singles, just-barely-yarn, then they will knit a straight rectangle, just one bar of the knit stitch will be straight up-and-down rather than the usual knit "V".
If you knit garter stitch (knit each row when knitting flat, knit 1 row, purl 1 row when knitting in the round) or seed stitch (k1p1 across row 1, even # stitches, k1p1 across row 2 on wrong side so K's are above P's and vice-versa) then the stitches will "even out" any bias in a high twist yarn and again, keep the work square and flat.
That said, active singles can give you some fun effects -- swirly socks, for example -- how cool would that be! with a garter stitch heel and a star-bind-off toe -- ooo the possibilities. And Spin-Off Spring 2006 had an article with cool zig-zag scarves knit from active singles.
Hats knit in the round may "swirl" a bit, but again - design feature!
FYI, If your singles, once washed, only twist around once in the skein when dried without weights, they are unlikely to bias when knit.
They're also great for crochet, nalbinding, pretty much whatever you want to do with them. I love felting my low-twist singles, either as yarn or in the finished item (clogs, tote bags, ...)
(posted by me on spindlers this day)