4 signs it's time to start from scratch:
1. You started using Lightroom and just started importing your photos from all over your computer and external hard drives (basically where ever you could find them at the time). You were excited right? I don't blame ya. But there was no real organization to the process and now its a mess - you feel like you're constantly seeing little question marks telling you the file can't be found and you have no idea where your photos really are.
2. You eventually got the hang of this "catalog" thing but only after you'd imported thousands of photos in haphazard ways. So now your catalog is half organized and half chaos. Almost like #1 above but not quite as bad - but still bad.
3. You started using Lightroom 2 and created a new catalog to import your photos into because you were afraid to commit and upgrade your catalog at the time. But eventually you upgraded your Lightroom 1 catalog to Lightroom 2. Now you have 2 catalogs and don't really know why or which one you like more. All you know is that there's 2 and you wish there were one.
4. You have 2, 3 or more catalogs in Lightroom because some one told you to create multiple catalogs. Now you hate it and find yourself really only using 1 catalog most of the time but don't know what to do about the others you created. Or worse yet, you've imported photos from those other catalogs into the main one you like so now they're in two places.
(note: I'm not saying multiple catalogs is a bad thing. I'm only suggesting that having multiple catalogs and not using them them is)
As promised, here are a few videos that talk more about catalogs, and folders, and organization and all that fun stuff:
*Lightroom Folders and Hard Drives
*Moving Between Laptop and Desktop
*Merging Multiple Lightroom Catalogs
*Organizing Photos By Date (and why not to)
*Moving Existing Folders
Where to store your photos in Lightroom
Finally, do me a favor and leave a comment with your thoughts on the topic. What kind of catalog issues/problems do you have (if any)?