What is the difference between unique user agents and unique sites?
I'm hosting a vbulletin forum with 25.000 members, with an average +/- 120 online members, and 200 online guests whole day long. When i look in webalizer under monthly statistics. It says unique sites: 90.000 and unique user agents: 3.600

Now, which number shows the actual amount of unique visitors? I don't get it :D

The user-agent would be their browser information, or how many different versions have accessed your website.

Examples:
Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.0.3) Gecko
Mozilla/5.0 (Windows; U; Windows NT 5.1; nl; rv:1.8.0.4) Gecko

I see, so unique sites = unique IP adresses. Thanks.