RewriteRule ^(.*)?$ tags/tags.php?name=$1 [NC,L]
This alone will rewrite everything to the tags/tags.php file.
You could use conditionals to exclude certain important paths.
RewriteCond %{REQUEST_URI} !^\/?accounts[.*]$ [NC]
RewriteRule ^(.*)?$ tags/tags.php?name=$1 [NC,L]
... i think the rewrite condition syntax is right but I haven't tested it ...
So everything in accounts/ is granted as expected and everything else routes to the tags file.
Depending on how complex your site is, this could be a good or bad idea. If your focus is on users and you have few other pages (like about, faq, contact, etc) then you should be fine. Otherwise you may be getting into a nightmare for conditional sorting.
I used tags.php as an example as well as /accounts. I don't know the structure of your site so I don't know your exact needs. This should be enough to get you started.
My point is that you might have to be ready to have a lot of conditionals above your tags.php htaccess rule since you are comparing against the first uri segment. If your hopeful path was more like www.yoursite.com/user/username it would be a lot easier.
