This is not anything new that can't be gleaned above, but just to clarify, if you have both versions of TextEdit installed because you don't want to delete the Lion version, there are at least two ways of getting a document to open with the old TextEdit when you double-click on it:

1) Option-control-click the document icon and set the document to "Always Open With" the old TextEdit. As noted above, you can't use the Get Info dialog to "Change All" TextEdit documents to open with the old TextEdit, it just reverts back to the new TextEdit, but you seem to be able to do it on a document-by-document basis

2) If the old TextEdit is _already open_, then double clicking on any document will open in it rather than launching the Lion TextEdit. If you set the old TextEdit to launch on login and discipline yourself not to quit it, that could work also.