there is no excuse to put an added annoyance/obstacle in the way of the user. just gets annoying to most people.
Solution: Reach into your pocket and pay for the bloody thing. Many who sulk about a measly payment for mIRC with the usual cries of "I can't afford it" are the same who'd happily put $20 worth of petrol in their fancy car and go for a tour of the local town centre at all hours of the night trying to impress their mates, or those who'd happily go and buy two packets of fags and kill their lungs prematurely, or go to a nightclub and pay the bouncer a 'tenner' to get in and then the druggo $50 for a deal.
If you want free software then get it, by all means, if you want mIRC (and some other clients) then it is not too much to ask that you don't cry crocodile tears about being asked to pay for it, even if, at the end of the day, you choose not to pay.
