Well, from time to time I've kinda wanted to address this issue anyway, so I'll hijack this thread and address it here. As a general rule, I think you probably wouldn't want to hijack someone's FTC thread or Showcase thread or For Sale or Wanted thread. And posting a lot of off topic messages in a Troubleshooting thread could make it hard to follow the diagnosis and treatment discussion, especially in a thread that might or could have eventually become a Must Reads selection. Some threads have not become Must Reads just for this reason. And I wouldn't think you would want to hijack a serial number thread, especially before Mica has had a chance to respond to the request. And you might not want to clutter up a Dreaming thread if there's an ongoing discussion about a probable custom order. And I would think that you wouldn't want to get too far off course in someone's Gigs thread. However, any thread that starts out by talking about bikes or beer should definitely be hijacked as soon as possible. Common sense and respect for fellow club members should generally be a good guide.
