It'd be nice if someone would bother to set up a site or a wiki to collect these ideas in one place. Call it "Please somebody make this" and bootstrap it by annoncing on HN :)
https://spreadsheets.google.com/ccc?key=0Ag-R_ZlGO21NdE9HSWR...
Also related: http://www.builditwith.me/
The problem with idea sheets seems to be that most ideas are terrible...