There is lots of news about Facebook. Everything from how it generated new sales and leads to the amount of time people waste at work and how it one of the latest tools for school bullies.
A recent posting on baseline magazine will give you some of the recent facebook numbers as it relates to business.
The link to the article is here:

http://www.baselinemag.com/c/a/Business-Intelligence/30-Fast-Facts-on-Facebook-at-Work-406941/?kc=EWWHNEMNL09132010STR1
We are not here to debate the merits of facebook; however, if you need to block it, I have included the instructions on how to block it using the NetSentron below. If you need a teacher, marketing department or the HR department to have access to facebook, while closing it to the rest of your network you would exempt that person or workstation from the filter.
The specific instructions on how to block facebook came from the following request:
The kids have discovered that if they go to https://www.facebook.com they can
bypasss the filter. From that point on even http://www.facebook.com and
facebook.ca is accessible. I need your help to block this.

null
First thing to do to block facebook is to blacklist the domains.
That would include facebook.com and facebook.ca.
That alone is not enough since kids will do all of the following:
1) Try a proxy server – they would go to another server that is not in the black list and then facebook from the proxy server.
The solution here is to block all the proxy servers. Netsentron administrators know how to do that. There is a checkbox to block all known proxy servers.
2) They could go to another facebook site. The students could try facebook in Germany or France or??.
Now we have to block all facebook domains.
Latest exploit the kids discovered to bypass the NetSentron filter:
Go to babelfish.yahoo.com enter in www.facebook.com and choose Greek to English,
voila you have access to facebook even though it is blocked.
The fix:
Go to Filters->Content Filter
Then click on “Edit Banned URL Expressions”
Scroll down the window to the very bottom (you should probably see #(proxy) as the last
line)
Add the following line
(facebook)
Click on “Update Banned URL Expressions”
Now, anytime that facebook shows up in the URL (which it does when you do a
translation on yahoo), the site should be blocked. This works even if YAHOO.COM is in
the exception list.
3) The students in the above case used https. It is a secure connection (like online banking) where we should not break into the middle of the online conversation. One way to fix that is to take control the proxy server. If we break into the middle it basically creates a ‘man in the middle attack’. We don’t want to look like a hacker – our job is to stop them!
The quick way to stop all traffic to facebook servers is to stop at the source. The final resolution was generated by Darren in our office:
Go to Firewall->IP Block
Add the two following entries:
TCP 69.63.176.0/20 1:65535 DROP BOTH
TCP 66.220.144.0/20 1:65535 DROP BOTH
This will block all current IP’s owned by Facebook.