After swearing by gear slings for the first 8 years of my climbing career, I gave them up because I noticed that none of the pro trad climbers, or friends, that inspire me, wear them. Now I will use one on easy ground up to 5.9 if we really have to boogie, if not it goes on my harness.
Racking on my harness keeps me more balanced and I don't have to keep adjusting the sling and throwing it around my back when all the cams slide forward everytime I lean forward. Plus, you can't drop the whole rack if one fumble...
It's totally your own perogative, but it's gotta mean something that i've never seen anyone lead hard trad with a gear sling.