First of all, let’s review what an Onclick textlink looks like, and why would someone use them.
As long as the onclick elements doesn’t change where the user goes and just track clicks, there shouldn’t be any problems. The real issue is where the onclick determines location–or worse, supercedes the href, or the href is blank.
Using the above example, the search engine sees the link text is “Carrie Underwood Undo It”. The span is just to put the song title in italics.
In summary, for SEO, it’s best to use the straightforward static HREF textlink whenever possible.