I built my fixie left-handed (by mistake: was doing it nekkid and wanted to keep the transmission away from my knackers!). It ran fine but looked weird - as weird as a single-side fork or other freakbike stuff. Nothing unscrewed, but it was all done up tight and I'm a bit of a threadlock ***** these days. The one problem: I have Time ATAC pedals and I couldn't clip in 'cos they were facing backwards!