I don't think I have ever seen explicit links at the end of chapters back to the TOC in a MOBI ebook. The reason for this is that MobiPocket Reader has a way to bring up the TOC at any point in the ebook. In the Windows version, select Contents -> Table of Contents. So the important step is to make sure your TOC is included in the guide items. In your case the TOC is presumably a separate HTML file. The current favorite approach seems to be to not include the TOC in the body of the reading flow at all (i.e. you must use the MOBI Reader to get to the TOC), or you can just link to the TOC at the start of the ebook (see the attached screenshot), or you can include the entire TOC near the start of the ebook (as well as in the guide). Badly formatted MOBIs either have no TOC, or only an in-line TOC (no guide item).
If you want to link back to the TOC, just include an explicit link in the HTML.
Last edited by wallcraft; 05-03-2009 at 08:32 AM.