There is a new update for Team Meat Super Meat Boy on Steam, which adds amongst other things a Beta Level editor and access to a portal to upload levels and chapters.
According to the official Team Meat site, the level editor lets you create anything you see in game minus bosses and warp zones, and is available from the Tool section in your Steam Library.
"The Level Editor saves locally, but you need to upload your level to the SMW portal for it to become active online. To do this click Upload, then complete the level to set the par and upload the level to the portal (to prove its possible you sadistic asshole!). REMEMBER TO SAVE YOUR LEVELS LOCALLY BEFORE UPLOADING!
The Level Editor supports FULL CHAPTER UPLOADS! to create a full chapter first you must make sure all of the level in your chapter are uploaded to the portal. Once you have done this click the "create" button to choose the ordering and number of levels in your chapter, you can also choose what music you want here as well. Once you are finished just click upload and your chapter will popup in SMW. Chapters must be over 5 levels long to upload.
The Level Editor supports a full playable character roster, without requiring you to have those characters unlocked in game. Click Meat Boys face icon to access the character chooser, once you choose who you want people to play as in your level/chapter hit F1 (to go into play mode) and the character will become active.
The Level Editor is in Beta, and probably will be for a very long time. This means there could be some minor issues we didn't find in testing, if you find any major ones please let us know in our forums so we can fix them in future updates. Remember to Save your levels locally (hitting save) very often incase of a crash, F9 is the shortcut key for save."