Following on from Jon Udell's post, as far as I can see (and I'm saying this because I like upcoming.org and I'd like it to be in a state where everyone could use it), upcoming.org isn't more popular because:
- It's a pain in the arse to enter new events. For example, the time's in 12hr am/pm format, with drop-down menus for each part. There doesn't have to be a full-blown API, but just a way to add an event from an external link like:
would make things a huge amount easier. The description and the venue would still have to be entered or chosen by hand, so there's still a barrier to spam.
- Related to the above point, there's no way to import a calendar event from another system. Say if someone sent me an email for an event with formatted data attached, I'd have to go and type that all in again into upcoming. I'm not sure there's a well-defined standard for transmission of calendar events like this yet though, so that's forgiveable.
- There are no moderators for each metro. For example, artist names are supposed to be separated by commas, but if someone doesn't follow those rules there's no way for someone else to fix it. Same with venue details -- if someone doesn't enter the address for a venue, or misspells the name, it's stuck like that forever.
- The map links only work for North America. It would be easy to fix that with a bookmarklet or GreaseMonkey script, but the system needs to know about different map servers for Europe, at least.
- And, of course, unlike Flickr or del.icio.us, there's no forum, mailing list or anywhere else to discuss things like this.