Should you use multi-site or multiple Drupal instances to host different content for subpath sites? I want to host a Drupal 7 site that effectively has four different silos of information. The architecture will look like this:


example.com - Blog site with content about the parent company
example.com/foo - Informational site about sub-company "foo"
example.com/bar - Informational site about sub-company "bar"
example.com/fubar - Informational site about sub-company "fubar"


The top site will pretty much be a blog with navigational elements directing people to the sub-sites. The three sub-sites will essentially be the same structure, but have slightly different CSS (different color schemes) and have different information. Logins can be separate, because we actually want to be able to peel away one of the subsites to sell as an asset, if need be.

I'm wondering what the best way to do this would be. Multi-site should keep it easy to update, because the modules and core should be upgraded in lockstep. However, I can't seem to get multi-site to work for these subpaths.

Is multi-site the best way to go here? Or should I just host four different instances of Drupal, one for each site?

(Note, I saw a question about subsites just after I posted this, but it seems that subsites is only available for Drupal 6. Please correct me if that is wrong!)
Subsites should work for Drupal 7 as well (assuming this is what you're working with).  I've found these instructions helpful in the past: http://drupal.org/documentation/install/multi-site

If the company subsites you are running are under one parent company where there is one body of management (a common decision maker), then subsites makes sense.  If they are different companies which may want very different functionalities for their sites, then it may not be wise to combine them into subsites which rely on the same code.