I noticed that the XPP library that’'s in use in Smack was last updated early 2005. There have been several releases since. I think the last one is this: http://www.extreme.indiana.edu/dist/java-repository/xpp3/jars/xpp3_min-1.1.4c.ja r (they got a quite confusing version numbering scheme - please double check this :S ).
I added the new library to a project that I created to test specific Openfire functions - those tests (which create about 300 Smack connections) ran fine.