I'm glad you brought that up.
Just as you can check a book out a second time, mIRC still continues to function after 30 days of use.
This isn't to say that you now have an excuse not to buy mIRC because Khaled doesn't forcefully remove its functionality from you... but rather that Khaled understands that a few people may have difficulty arranging $20 of expendable income in just 30 days.
The reason a progress bar was added to 6.10 is because, as people have plainly stated on this forum, many users didn't realize that mIRC was Shareware and not Freeware. The sudden panic that mIRC might cease to function after 30 days is a clear indication of people's reluctance to pay money for software. It's safe to say that many of them wouldn't register unless they thought it would cease to function. For everybody else, the checkbox was removed from the about dialog to grind away at your nerve and conscience until you finally break down and purchase it.
Perhaps books should have progress bars too.