... and that's what we're trying to do !
I wouldn't say community is the weak link for MODx : quite the contrary !
We have a really great user base : of course we can't compare to Joomla or Drupal (in term of user base) which are way older projects but I think the interresting point is the very high quality contributors and the great spirit there is @ the MODx forums

People are helping each other in a way I had only experienced with the Textpattern's forum, back in the good days...
The challenge will be to keep it that way while continuing to grow. A too wide user base too soon could hurt the project, I have been convinced of this ever since I joined in 2005. I don't think we should try to become the Joomla or Drupal community.
At this stage, we need early adopters, reknowned designers and skilled devs. I don't mean to say we shouldn't try to attract more users, but that we should only go marketing for the end users when we are done with severing ties to the legacy Etomite codebase (here is our weak link, really). That would be somewhere between 0.9.7 and 1.0.
We'll get there but you'll have to wait a bit. 0.9.7 will be a great jump which will require momentuum in the coders / adavanced users / early adopters community : converting existing addons, creating new will be key which means writing those and testing those. MODx won't be the thing for those who await a pre-packaged solution (IMHO). My reading of the upcoming marketing challenge will be to attract more coders as the framework aspect of MODx gets more prominent, and get more skilled testers and early adopters / promoters to spread the word. It means a well defined target, and adapted communication channels and messages. We're working on that.
Now about MODx being a competitor to Joomla or Drupal : we already are !!!
Even with less maturity, 90% of what you can achieve with Joomla or Drupal can not only be done with MODx, but more efficiently ! If you need revisionning, or elaborated workflow, I won't argue : MODx needs to fill the gap. But in all other areas, we compete and ask a few people coming from Drupal or Joomla : we do better customization and flexibility-wise, by a BIG margin !
For designers, it's a dream come true : templating is really easy and MODx adapts to your workflow, not the other way around... don't get me started on template variables and what can be achieved with MODx ! (ok, Drupal has the CCK module but... not as good as TVs IMHO). I like not being forced into a content structure, and so do my clients ! Custom content structures are easy.
I think those who think "we'll be a great competitor" are wrong, "we are great competitors" already

(yeah, well, maybe not tactful but true

)
This is not yet widely known, and that's on purpose, but more and more come to us and are silently switching...
Wait and see !