Some time ago I downloaded an irssi script called keepnick.pl. This script would use the IRC command ISON to check if your desired nick is in use when you connect. If it is, it will keep checking periodically and use the NICK command once the nick is free for you to take it.
Since this can take a while and the other guy can do god-knows-what with your nick during that time, NickServ was invented long ago. Granted, some braindead networks (*cough*IRCnet*cough*) still don't use that, but one should stay clear of those anyway.

I then expanded that script to include support for the NickServ GHOST command. This way, you can force a disconnect for a given nickname using a password you registered before. So, now you can do this, for example on freenode:
/keepnick -net freenode -nickserv NickServ services. mysecretpassword mynickname

Now, when a request to identify comes from the user NickServ@services. (and only that, NickServ@some.hostname.foo will not be accepted!) then the command IDENTIFY mysecretpassword will be sent.
On the other hand, if your hostname is in use, the command GHOST mynickname mysecretpassword will be sent.


The script is available on my non-blog website.