There are no best practices for using tags?
Not sure if it a best proatices, but this works for us.
You can have your link to an editor add a tag. This makes sure the tag is not forgotten and is consistant. IOnce you have a know tag, you can set the RSS feed to display items with that tag. it is handy for items such as a help request. Adding the document template widget also enables you to have common text in the body.
To find out what terms are enered into the search field needs a support ticket (hosted at Jive). May not help with tags but can be useful for organization, help articles, etc.
If you have access to the Analytics module (thus access to the Analytics database) you can certainly get the search metadata to examine. Below is a SQL query I use at the start of each month to examine what the top user search phrases were. From there I typically look to see if there are some new phrases/words that might not be captured already. After figuring that out, I look to tags we have on our content for any updates that need to be made. Right now it is a bit of a manual process but completely doable.
select metadata, count(activity_ts) as "Count"
where activity_type = '170' and activity_ts >= '01/01/2011' and activity_ts < '02/01/2011'
group by metadata
order by "Count" desc
I am not sure if there is a limit on the # of tags but I do know we have some items with 30+ tags. I honestly haven't assessed if that hurts/helps but it is certainly possible.