Shoutbox

I may not be a 1337 coder, but I can have a stab as to why Plus has to be running first.

In order for Plus DLLs to intercept certain parts of Messenger's own workings (to apply text formatting for example), the callback address of the event has to be overridden so it points to Plus's version.
This is best done as the program code is loaded into memory. Changing once program execution begins is dangerous, especially in multi-threaded apps, as you can't predict where the instruction pointer is.

Anyway, that's how I understand it.