Recently I was working with one of my customers they had setup Web Analytics in SharePoint 2010, and wanted to test how effective it was. They started running a script against the environment that made web connections to a ton of pages and documents and lists as a single user, having the script make approx. 120,000 connections they figured they should have seen a ton of data to work with.
When they brought this to me I had to explain that Web Analytics in SharePoint 2010 only does page hits (This changes in SharePoint 2013 but more of that later). So I had them setup the script to hit one single page and figured we would see a massive spike just like we wanted to. Waited till the next day and went to look at the site report and it had almost nothing, zilch, nada we didn't understand we couldn't explain it. So I started to dig searching thru RFC's to the product group, old cases, and unfinished KB's till I finally tripped over an RFC explaining the behavior. Enter stage left the lost rule, it seems the product group built a Spam rule into the product to remove what they believe would have to be bots or other non-user behavior.
The Lost Rule:
If Web Analytics sees more then 1000 clicks from a single IP address or a single user within a 6 hour period of time. The data will be detected as SPAM and removed from the staging database and not processed further.
So we had setup another test where we had a single user hit one page 800 times, and the next day the site report showed us every single beautiful hit. I have also discovered that there is no way to turn off this rule or change.