No problem.
1. No harm, no foul. I like the appearance of the ; start. Doesn't bother me to use it, and is more of a visual queue to myself that it is infact commentary.
2. I'm a programmer of multiple backgrounds. I use what is the most 'generic'. Not everything I write accepts elseif, and as such i find myself using else if more so.
3. Touche'. Again, comes from doing a lot of other languages. Most recently, I've been trying to complete a web site in php, and using functions such as is_numeric. I never thought of the isnum condition honestly. Noted, and recalled.
4. I thought about it, but it's been my philosophy that unless it really matters, encode/decode will do. Additionally, giving the nature of the bot, its purpose, and implimentation, I went on the basis that providing the ability to retrieve the password would be a sort of undocumented feature. If this script served as a different purpose, I would have used $md5.
Thanks for the critisism, and happy coding.
