Been using a Moleskine notebook with a fountain pen for work notes--the results have been most unpleasant! The Bleed through and Show through is horrendous. I doubt I'll try that combination again, or at least forego using both sides of a sheet. Probably less of an issue with a ballpoint (one hopes) but I'd be leery...
RayFI use a Moleskine day planner with a ballpoint and no issues with bleed through, writing on both sides. It did bleed with both a roller and a fountain pen though.