After reading about it somewhere (Macintoshian Achaia, perhaps?) I plopped down $12 on Bookit this morning. Converts to/from many web browsers, including OW -> Safari. And, wonder of wonders, it preserves everything beautifully. OW uses HTML for its bookmarks, so "ó" (for instance) becomes its corresponding HTML entity "& oacute;" (minus the space) when Safari's in-app bookmark importer runs. Bookit converts this (and other entities, like ampersand) properly. It's great, and it's cheap. Once it's open, assuming you're doing OW -> Safari every time, you can do the whole conversion just by hitting enter a few times - nothing to click.
http://www.everydaysoftware.net/bookit/
HTH --