I got this from a guy who re-carpets boats.
Mineral spirits won't evaporate as fast as more volatile (and flammable) solvents and it won't damage the finish under your carpet. The slow evaporation rate gives it time to soak in and soften the glue and allows you time to scrape or scour the glue completely off. Buy a small can and try it.
I can't believe some of the dangerous and useless (Goo Gone) recommendations on here.