For starters, the original poster should have said "IRC" instead of mIRC.
mIRC (a chat software) is just one of the many ways to use IRC (a chat system). mike named another option: xchat. Anyway, as I'll show you, people don't even need to know what these letters mean to open the op's chatroom.
People still use IRC in general?
A lot of them do. Check the current number of people online in the biggest networks on the "IRCSearch" site. It usually is around one million users.
Currently, IRC is heavily being used for technical discussions (like community support for programmers, users of open source softwares and wikis etc.), but the major servers still have lots of general topic rooms, including Christianity - use the IRCSearch to search for "Christian". Today, one can also use IRC to connect to other services - for example, to download big files like Japanese cartoons, to use their MSN and Yahoo messenger accounts with something called Bitlbee, or to update their Twitter profile with Mibbit.
Thanks to Mibbit, a customizable and safe IRC client that works on your browser, people now can access IRC rooms even from computers protected by firewalls, and put "widgets" on their sites and blogs for friends to join the chat. I haven't tried the OC.net chat yet, but this "widget" could replace it someday for free, if needed.
Unfortunately, Undernet (the server used by Don-Romania) is among the few large networks that don't support Mibbit officially, and they limit the number of web users. You can give it a try to open the op's room anyway: http://mibbit.com/?server=irc.undernet.org&channel=unity
If it gives you a "too many connections error", you can at least have an idea how it looks like simply by accessing a room on a supported server: http://mibbit.com/?server=irc.mibbit.com&channel=testroom
(if you don't like the colours, don't worry, everything can be changed, from the fonts to the smilies).
In short, IRC is alive and kicking, and now is simpler, more useful and safer than it used to be 10 years ago. :p