What should I use to remove sticky mousepad residue from a desk?

Use isopropyl alcohol (70% or higher) — it dissolves adhesive without damaging most desk finishes. Dab a microfiber cloth with alcohol, let it sit on the gunk for 20–30 seconds, then rub gently in circles. Avoid acetone, bleach, citrus cleaners, and magic erasers. In a pinch, cooking oil works too.