Okey :)
However, if you are creating an if statement just to force the else when certain conditions don't exist, you should just use !isin instead of isin and != instead of ==.

Like this:

if ((http://twitter.com/ !isin %mirc.temp) && (tweet-url !isin %mirc.temp) && (%twitter-maxposts != $iif(!%twitter-reads,3,%twitter-reads))) {
   msg %twitter-channel  00,02Twitter: ( $+ $remove(%twitter-connection,/) $+ ) $replace($remove(%mirc.temp,<span class="entry-content">,</span>),&gt;,>,&lt;,<,&amp;,&)
   inc %twitter-maxposts
}

By the way, you still left the variable %mirc.temp set. If you don't declare the variable as local before you sockread to it, it's automatically declared as global.

This is the proper way to do it with a local variable.

var %mirc.temp | sockread %mirc.temp