I got this from Knitty.com....works like a charm
Avoiding the jog
If you merrily knit around, doing nothing but changing colors according to your whims [or mine] you will have a slight misalignment of the stripes at the beginning of your round. It looks like the stripes are higher on one side than the other -- and they are: you are knitting a spiral. You may not care, but if you do, try this:
Change colors and knit the first round with your new color. When you come back to the first stitch of the new color [first stitch of the round] pick up the stitch below it, [it will be your old color] put it on the left needle in front of the first stitch of the top row, knit them together and carry on normally. if you are not changing colors, don't do anything. Try an Internet search on "jogless jog" for more information.