SBS 2011 - How can I monitor website and social networking use?

This is only possible if your gateway/firewall has the ability to log URL traffic.  This is usually the case if your gateway/firewall has proxy functionality.

If it does not, you'll want to install a proxy server that all web traffic will flow through in order to capture the logs.

To add;  most routers, even inexpensive ones, have the ability to output basic traffic monitoring to a "Syslog Server" (logging software).  There are many of these available, one free one is:
http://www.whatsupgold.com/free-software/network-tools/syslog-server.aspx
This should monitor the type of traffic and IP.  You will have to lookup the IP (nslookup) to see the domain name of the site visited.

Will this do what I need?  

http://www.newegg.com/Product/Product.aspx?Item=N82E16833181137

I would need a report by user or IP on hours/mins spent on specific websites.

I don't believe so.  Though a lot of nice features for the price it seems to offer; bandwith management, site restrictions, and will log access to unapproved sites but appears to only do so by category, such as education, gaming, etc.   This would also only work if the ZyWall service recognizes the site.  There does not appear to be any monitoring of specific sites, users, or IP's.  A proxy server is best for detailed monitoring and reporting such as you are asking for.

you can consider this for SMBs enviroment - Sonic TZ100  - sub $300 (excluding services)

http://www.sonicwall.com/us/products/TZ_100.html#tab=overview

http://www.sonicwall.com/us/products/Network_Security_Comprehensive_Gateway_Security_Suite.html#tab=cfs

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