This particular one, the Disposal Genie, I saw on Ask This Old House and looks to be simple but effective in keeping things from inadvertently going down the sink like utensils. For the hazard prone it will also help keep hands (other appendages?) out too! The Genie has a food scraper there too which may or may not come in handy, I am undecided on that one.
For those who want some flair the Disposal Genie also comes in red, blue, and green.
Red - http://www.amazon.com/Danco-9d00010451-Disposal-Genie-Microban/dp/B004XWWIT2/ref=pd_cp_hi_2
Blue - http://www.amazon.com/Danco-9d00010452-Disposal-Genie-Microban/dp/B004XWZS08/ref=pd_sim_k_4
Green - http://www.amazon.com/Danco-9d00010453-Disposal-Genie-Microban/dp/B004XX0GG8/ref=pd_cp_hi_2