One thing I find myself constantly needing is a way of doing an 'if not' test in templates, not just an 'if' test. I know that something like <% if ! whatever %> or <% if not whatever %> is not valid, but I'm sure there must be some way round this which people use. The only solution I have at the moment is to have a positive test then stick the code I want to run in the <% else_if ... %> branch, which is inelegant to say the least. What do more experienced SilverStripers do?
Incidentally, I'm sorry if this has come up a lot before (I'm sure it must have), but it's a very difficult one to search for because of the nature of the keywords.