What is wf.xml, and should I remove it?

It is an Excel 2004 spreadsheet. Do a backup. Try opening it to see what it contains and then decide if you want to delete it. Or just delete it.

You are welcome.

Just to avoid possible future confusion, an Excel spreadsheet is .xls for Office 2004 or earlier, and .xlsx for Office 2008 or 2011 (Mac versions). They're the same two extensions for the Windows versions of Excel, I just don't know which years for sure they changed without looking it up. I think it was Office 2010 for Windows when it went from .xls to .xlsx.

Anyway, an .xml file means (eXtensible Markup Language). Which is a file type used by many apps to save data. You can view them as text with TextWrangler if you want to see what's in them. It's essentially the same file format as Apple's .plist files. If you used an app like EasyFind to search for .xml on your drive, you'd find tons of them. OS X installs quite a few of them itself.

Can't say with any kind of certainty what app produced the file you found, but it would be harmless.

Kurt, I just checked with EasyFind and it found 450 of em: files, docs, plists, etc. Like you said, most (or all) harmless as far as we know.

Yup, for the most part, XML data is nothing more than settings data. All kinds of apps use it. For each Nikon RAW .nef image you do changes to, it saves the changes as a .xmp file. But if you view that file, part of the first couple of lines note that it's XML data:

<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 5.5-c002 1.148022, 2012/07/15-18:06:45 ">

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">

The same thing is noted at the top of any .plist file:

<?xml version="1.0" encoding="UTF-8"?>