I find the fact that MyBB doesn't allow multiple consecutive spaces in posts a little annoying.
Typical English says that sentences should be separated by double spaces - I typically like typing like that, however, MyBB's parser doesn't allow it.
For example, typing:
will actually produce (by default):
Also, double spacing also allows other useful things, such as gaps between images etc.
This is a very simple plugin which will fix up double spaces. Be aware that if you have any custom MyCodes, that you don't put double spaces in them! ( won't be parsed).