Currently, mIRC uses a default port range of 1024-5000 for establishing DCC connections. Many modern operating systems (including Windows Vista and 7) have stopped using this range for dynamic connections and now use the IANA suggested range of 49152-65535. I think it would be appropriate for mIRC to start using this range by default, especially with the introduction of uPnP support.

Also, "randomize ports" ought to be enabled by default.