I find myself sharing little travelogues and/or pictures for about 1/3 to 1/2 of my outings. These writings picked up where I left off as I used to do such reports for friends via email. The writing for me has always been cathartic rather than narcissistic and thanks to yahoo letting us save pretty much unlimited emails, it is something to look back on here and there.
That said, narcissism has a rotten connotation and I'd quickly bow out of the writing game if it ever became a common belief that those of us who choose to write about our adventures were doing so out of sheer narcissism.
