Also, just some tips:
-Arans and Lacy sweaters need to be done flat, because they need that seam for stability, plus, if you knit an aran in the round, that's a huge piece to haul around on a circular needle, especially up near the neck.
-Fair isles and colorwork (not intarsia) sweaters need to be done in the round, because you can always see the pattern.
Anything else, like plain stockinette, texture, or a small cable panel, can easily be converted to knitting in the round. It's just a matter of figuring out patterns, and working out the stitches.