No one denies the power and goodness of Lisp. Also, everybody knows its issues
1) misconceptions based on its history (it's a slow, AI language)
2) portability issues among implementations (pathnames, sockets, GUI, etc
3) lack of standard implementation
#1 is a marketing problem - tractable with effort (just look what pg's essays alone have done). #2 is a coding resource problem - many hands make light work.
For #3, once there is a platform implementation with all the right features (threads, unicode), this problem goes away. If CLisp added threads or if SBCL worked on Windows, the game would be over - other implementations would continue but there would be an unambiguous choice for n00bs. De facto portability standards would form around that implementation and the burden would be on other implementations would make it compatible with the de facto winner.
I'm not invested in any of the implementations but it looks to me like SBCL is the closest to being the full featured, cross platform, open source implementation that is currently lacking. So as a pragmatist wanting Lisp to become bigger, I have three choices:
1) through my writing, encourage people to choose SBCL
2) contribute coding help to the SBCL windows port
3) whine
Most people choose #3. I'm not confident in my coding chops to do #2, so I'm focusing on #1. I have the time and ability to write well and I hope to add momentum to the front runner and make choices easier for new users.
Of course, the foolproof way is for someone to make something indispensable using Lisp so people can't help but adopt it (like Unix/Linux did for C).
-see also Bill Clementson's take on this from a couple years ago http://bc.tech.coop/blog/060403.html