All the OmniGraffle users out there will want to check out Todd Moy's list of tips and tricks that all OG power users need to know. The character replacement one in particular will save you time. Although I tend to just clone an entire object's style the style brush with W and OPT+W, you should definitely learn about cloning discrete styles with chicklets. You'll wonder you never did.
Check them all out on Viget Advance and level up your OG skills.