Since CraftBukkit already reads the filename for each plugin why don't you change the error to say what plugin is being read at the time. For example today i tried to install the jail plugin and instead of saying "Server: Can't run Jail.jar" and move on it say: "Jan 26, 2011 10:56:38 AM org.bukkit.craftbukkit.CraftServer loadPlugins". To me its not very useful that way. If a severhost is trying to get 5 different plugins installed they are going to have to go through each one to figure out what works and what doesn't.
