@Agenda
To keep information for reference about things you have discussed with somebody, it might just suffice to use the notes field in the address book.
To keep track of things I need to follow up on, I create new "to do" entry with the name of the person involved and the subject, and use @WaitingFor or @Agenda as the category depending on the subject. I normally use @Agenda for people who I deal with regularly as well as for those with whom I meet only ocassionally.
I use Agendus instead of the original Palm apps. When listing meetings or "to dos" it includes the name of the contact in a different colour. It is also possible to see all the meetings and "to dos" associated with a contact from the address book. It is useful to have this log for interactions with someone.
I have used at times a nice application called 2Action Meeting. This lets you keep a record of meetings, including those present, notes, topics and "to dos" arising from the meeting. The "to dos" can be linked to the Palm "to do" list. The topics however, cannot be linked to,say, "to do" @Agenda. This is the reason why I now just use Agendus.