Well, these came to my mind recently, and it seemed like a good idea to ask around :)
1-Did Sony ever charged a monthly/yearly fee for the NY member site after the first year? (IIRC they said they might do so, but AFAIK they never did)
2-Was there a storage limit imposed to member's pages? If so, what was it?
3-Did members have to share the source code of their games/apps? Or was this optional?
4-Did Sony remove member's pages that were inactive or not updated in a certain period of time?
5-Most (if not all) Net Yaroze games included in OPSM UK were in FPC format. Is there any information available on this file format? Is it just a container?
6-Was any Net Yaroze game included in OPSM US? If so, does anyone have a list?
7-Did any Net Yaroze game use Audio CD? (mainly asking for the ones included in OPSM UK)
That's it for now; I may come up with some more in the future.
PS: There's no "post icon" for a Net Yaroze (ie. black PS1)