Apple

4. Sometimes, say with scripts activated by cron, one script will overrun its allotted time and attempt to run again while the previous instance is still active

Seems like a script with that problem is either running very often or taking a long time. If it's frequent and regular, why not use "on idle" and a stay-open script?

5. If two scripts try to tell the same application to do two different things at the same time (and nothing is done to stop one of them) the results will be unfortunate (and possibly make the scripter appear foolish in the eyes of his coworkers)

I can think of lots of workarounds for statement 5, but it seems to me I shouldn't have to. At the moment, I make sure to run all the scripts that use certain applications from one master script application that itself runs every few minutes (and only if System Events tells it that it isn't already running.) But I'd prefer to group my scripts by what they do, not by which application they happen to make use of to do it.

Depending on how many functions of a given app you're dealing with, it may make sense to write your own "with transaction" wrapper for the app - a single script that interacts with that application, basically passing through any incoming requests and passing back the results, but with a little added intelligence to queue the requests and avoid conflicts. Your other scripts, grouped however you prefer, would then communicate with this intermediary rather than directly with the application.