> > Also, is there an easy way, if any, to have cron not run a 
> job if the
> > last instance of that job is still running? Or would a 
> little external
> > logic be in order?
> 
> besides implementing locking, you could have the exit of one job
> schedule the next with "at" or bypass cron and just invoke 
> the next job
> directly, or maybe use "batch" so jobs won't be spawned if the load
> average is too high.

Unix Aphorism #42 "cron is not a scipting tool"

Cron should call a script. That script should check to see if it is okay to
run.