If you're using a shared Web host, one of the problems you might encounter is that some plug-ins expand CPU and/or RAM use beyond what they'll support for as single user. The usual solution is to disable one or more plug-ins and test and test and test again. Not very efficient.
How about a plug-in that could record what other plug-ins are using in terms of resources and database queries so one can diagnose this problem more readily and see which ones are hogging a system.
Can anyone deliver such a solution? Is it possible?