Great topic Bob.
The takeaway is, like your other public behaviors – your manner of speaking, the clothes you wear, your dental hygiene (!) – your mug, your visage is a critical component of your online presentation and identity.
As in person, your acquaintances' first image of you greatly affects their "sizing-up" process, which we all engage in. True, your ultimate content and personality can help that or further hurt that, but why not start off on the right foot, rather than tripping over it?
Also, a weak self-portrait can be just as distracting as a garish or incomprehensible picture or symbol. The classic "up against the wall and shoot me" faces are still out there (perhaps holding an issue of today's paper under their chin would complete the theme) and right away I'm turned off. I thinks that's a natural and understandable reaction from anyone.
Other images – snapshots of the whole family... in the distance – are among my other pet peeves. Do you have any "favorites?"
Finally, in the spirit of good visual branding, people should consider committing to a logo in the corner, an overall color tint, a colored bar...some consistent device which will still accommodate a changing portrait.
Oh...and did I mention that I wrote a very similar post on my own blog (http://lin.cr/fln) last night?