An annoying thing with SMB's leaderboards is that they contain loads of 0'00 and other buggy/hacked records, making it hard to find out what is the best possible time on each level.
Good news is I just found this list:Super Meat Boy record list on SpeedDemosArchive.com
It's quite old so I'm pretty sure a lot of records have been beaten since, but at least it gives some good target times for those who want to perfect their skills. There are both "fully legit Meat Boy records" and a partial list of records made with any character (usually taking advantage of Naija/Runman glitches).
I hope this helps!
EDIT: While I'm at it, here's a link to Super Meat Stats
, a useful tool to locate bandags/warpzones & monitor your progress towards the Rare/Medium Rare/etc. achievements.