Personally I used to not add a space but in recent months I've decided it makes the code look a lot tidier and more conventional. It doesn't bother me if people don't, but I think it always looks nicer if people do.
You're twisting things, short! I don't often put a space, but then again I don't pay much attention to the possibility of a space there. Zend actually gives me a space automatically if I press tab on the autocomplete list, but I tend to type them all myself and keep well away from the tab.
The man who comes back through the Door in the Wall will never be quite the same as the man who went out.
I generally (note: not always as there are exceptions!) follow the idea of adding a space between language construct and opening parenthesis, and no space between function name and opening parenthesis. That's always true for functions, but I commonly neglect the space for isset/unset/empty and probably some others that my mind doesn't want to conjure up at this moment.
Back to the original poll question, I always add a space after if, else, while and for. (Note: if you ever see code from me without that space, don't shoot me. It's likely just a typing mistake.)