I also think that $20 is a very small price to pay. I'd imagine only poor people and children would be unable to pay the $20, and poor people would more than likely not have a computer or internet connection.
- There's plenty of places where the economy compares poorly in comparison to Britain and the US where internet is priced appropriately for people in that country but the conversion into US dollars or British Pounds makes $20 an expensive proposition. In even poorer regions communal internet access is often available and in the future there's also government schemes like the OLPC project that would provide people with computers and internet access but not necessarily the means to spend $20 on software.
RusselB is overthinking the situation. The day would be by British/UTC time, as all past date-specific promotions have been for mIRC AFAIK (ie. charity months). Past registrations on the date wouldn't be retroactively discounted, why would they be? No-one could reasonably expect otherwise.
Regardless of all that though, I don't think the birthday idea is really necessary. mIRC already allows people to pay an amount lower than $20 if they decide it's too much, so effectively what the OP is suggesting has already been implemented for every single day of the year! Can't say much fairer than that.
