I'm assuming that you wish to set up online storage for ISP customers. I'm not sure what level of discussion you're looking for here, so please excuse if I tell you stuff you already know.

Pros:
Since it's based on HTTP, it goes through firewalls.
You can use all the same authentication techniques your Web server does, as well as SSL.
Very easy to set up, particularly with Debian/Apache 2
Stateless, so clients can keep the share mounted even offline.
Setting up a new share is as easy as setting up a new site.

Cons:
Security-wise, it's only as good as your Web server.
Not sure how it scales up, performance-wise. Presumably if your Web server can handle the traffic,
you'll be okay.


Sorry to not be more specific. Naturally, you'll want to set up a pilot server, beat on that for a while and
analyze the results. Depending on the sort of files people store on the share, you'll probably get more HTTP traffic on average.