Probably incorrectly, but I always suspected the introduction of Nintendo's "Vs. Tennis" and various "Vs." sports games...oh, about 30 years ago when I was in college and hanging around the student union's video arcade...as the cause for people using versing and versed:
http://www.arcade-museum.com/game_detail.php?game_id=10372
Tom
The first time I heard one of my children use this - some time in early elementary, in relation to a soccer game ("what team are we versing this weekend?"), I was excited to catch an example of back-formation in the wild! Something I had learned in my Historical Linguistics class (~1984) was happening in front of my eyes. I had no idea it had such a wide use, although since then I've heard numerous kids use it with high frequency. (Same child used to say "Kick" for a single piece of Kix cereal when he was a toddler.)
And quite coincidentally, just last night I heard a fitness instructor say "bicep." I wanted to let her know it was incorrect, but held my tongue...
No more than 30 days ago did I have talk with my 12 year old regarding his frequent use of "versing" and how that word is simply not a word (and grating to my ears!). After hearing this episode I've had a change of heart, and he's resolved to continue to use the word at home and around friends, but to keep it out of school papers and formal conversations. I always appreciate how Grant reminds us that words can change meaning and usage over time, and how Martha sees every improperly used term as a learning opportunity for everyone. Thanks for resolving another family word-usage squabble!