Pay particular attention to the link at the bottom of the 2nd link here.
I live in Tennessee, which is one of the states that are 'covered' by the program for State filing. of single-member LLCs. The answer is a mixed bag. You can basically have unlimited single member LLCs on schedule C's at the Federal Level. The problem in Tennessee (and other similar states I presume), is that you can only file ONE single member return at the state level. So, I can file 2 or more schedule C's at federal level, but at my state level I can file ONE single member LLC thru ProSeries Professional, and I have to manually file any additional Single Memebr LLCs at the state level on my Tenn Dept of Revenue website.