While creating a page that used server side includes, I ran into some very strange behavior. Right before each SSI, a blank line would appear on the page. It didn't have anything to do with margins or padding. It was just like an empty line appeared right out of nowhere, messing up the layout. First, I thought it was some problem with IIS and SSI, but I couldn't find anything there.
After a few hours of frustration and trying the weirdest solutions I could think of, I started playing around with saving the include files with different file names. Well, when I got to the *.txt, I noticed that Visual Studio gives me a new option under "Save As"... its "Advanced Save Options". When I looked at the encoding of the file, it was set to "Unicode (UTF-8 with signature) - Codepage 65000". I then switched to "Unicode (UTF-8 without signature) - Codepage 65001", and the blank lines disappeared.
It appears that Visual Studio picks an encoding when saving pages that doesn't really produce desirable effects when using server side includes. However, you can go to File -> Advanced Save Options and select a different encoding. I'm not sure how to set the one w/o signature as the default yet, but hopefully soon I'll figure that out :)