This is a generic reply to some of the more negative comments in this thread.
In the whole, mIRC is relatively easy to use. It has (in my opinion) very easy to naviage menu systems, and very simple and well layed out (for the most part) dialogs.
The help file could be better (but that is pure opinion, and mine at that), but it is useable, and does point out how to do things.
I should also point out, that a very well planned UI will always be a pleasure to use, and "minimalistic" (ie, tries to minimise the amount of clicking or typing to be done by the user).
If a dialog is well planned, and properly implemented, it will be effortless to use.
I should also point out that there will always be circumstances in which popups, dialogs, or commandsets will need to be used. When this is the case, one can usually find an equivalent command for it, or a method to make it quicker.
As it stands, mIRC is quite a capable piece of softare, from both a UI perspective, and a developer perspective.
If you can't find your way around it, then you shouldn't be using computers.