Throttle Body Spacer

Does anyone have any experience with Throttle Body Spacers? Are they worth the effort? I've heard that some spacers have side effects, such as a whistling noise. I'd like to install one if there isn't any ill effects, but not sure which type/brand to go with. My Sonoma has the 4.3L Vortec.

Thanks!

Won't help, the only engine proven to get gains are chevy 350's.

Complete 100% waste of money.

Put money into a new high performance muffler and intake upgrade.