This is purely a suggestion and doesn't need to be implemented. But it might be something useful if it were.
A quick switch function, where pressing a certain key combo (like alt+g) would bring up a small input box in the center of the client window. As users type into the input box, a list of open windows (chan, custom, privmsg, server) is presented and filtered down as the user types until a match is found. When the user hits the enter key, the input is immediately dismissed and focus is switched to the suggested window. A function like this would be immensely useful for any user who is connected to two or more networks.
For privmsg and channel windows, they would be appended with the server window name (I.E: for a privmsg to QueenElsa on Undernet, the suggested list would display Undernet.QueenElsa; for a channel #adiirc on Freenode, it'd display Freenode.#adiirc)
The quick switch would honor the user's network name from the server list. (If the use label as network name option is enabled for that given network.)
Anyway, just some food for thought for the future. :)