It's happened two out of two times (the statistics aren't great, but a trend is indicated). Launchd (under 10.4.3) property list that ran fine initially, starts to "go haywire" when niced by Launchd Editor. One plist was for a cron-like process, the other of the watched-folder variety. In both cases, they were well-behaived, but I decided to maximize their "niceness" (slider in Launchd Editor slid to the far right). And in both cases, as soon as they were re-loaded and re-triggered (based on their respective criteria), the processes ran, and restarted, and ran again, and again, and again, and repeated this infinitely... until I unloaded them (I noticed the problem in each case when the pegged CPU got hot enough to trigger my PowerBook's fan). Maybe it's a bug in launchd, or your editor. I don't know. Since my two situations both involve commands that can be niced from within, I've elected to go that route.

It's a good start, but it feels more like a beta release than something numbered v1.0.1 (however, I did pay my $5 shareware fee, so I'm "betting" on it turning out very good).