Conjunction Malfunction
for, and, nor, but, or, yet, so -- The traditional list of conjunctions.[1]
Technically "coordinating" conjunctions, the words in that list are meant to go between clauses inside a sentence. Starting a sentence with one of these is jarring to some folks who like words. Sometimes, of course, "jarring" is the effect you want, but that technique is best used sparingly, for fear that people will decide you just have no idea what you are doing.
A Wiki is particularly susceptible to sentences beginning with conjunctions because many edits are notions being tacked-on to existing text. The instinct is to add the change as a new sentence, even if it really is extending a thought in the original sentence.
Conjunction Malfunctions are easy enough to fix, but it makes things a little more enjoyable if they just don't happen to begin with.