There needs to be a version dedicated to bug fixes only. Aside from that the people that Khaled lets beta-test mIRC need to do a more thorough job. Test mIRC on all operating systems that it is designed for, test mIRC's ability to do the simple things like joining rooms but also more technical things that are still commonly used such as bans (remember the ban bug in V5.71 - it would always set a domain ban regardless of the type selected) and the current timestamp issue for those living in areas that have daylight savings. These are things that testers should notice before a release.
As for sluggishness, I haven't noticed it though mIRC is around twice the size it used to be and the more complex the code the longer it will take to execute. A couple of questions that could be added to this discussion are: Is mIRC now too complex and feature-rich to be able to do a decent bugfix? and: If mIRC is sluggish to some people, is it being developed in the best environment and using the best programming langauge possible?