Request: Guidance on Our Tagging System

We're working to make some adjustments to the tagging system in Social Roots. The problem is that there are a number of different approaches to tagging as it stands. I'll dump them into two categories:

• Delicious Model - this approach pretty much doesn't allow spaces in tags but does allow you to combine tags and to have nice, usable URLs. This is the model we have used.
• Flickr Model - this approach allows for more "wordy" tags but also doesn't really give the option to combine them.

Of course, now that we have been letting some people use the system, we're seeing lots of interesting behavior in the tagging input that has happened. We find now that we're want some guidance from the community as to what we should consider the right behavior.

• Tags will be converted to all lowercase
• Tags are delimited by spaces - commas are converted automatically to spaces
• Tags can contain any alphanumeric character and the hyphen, underscore, and colon
  Commas and plusses are converted to spaces automatically
• Tags are limited to 10 for a specific profile

Have you worked on a system like this? Do you have preferences for how it should work? Let us know.