Not part of any blacklist:
Nor triggers any virustotal warnings.
All reports claiming malware are fact free and misleading.
Not part of firewall blacklist:
It will track your IP address by calling a url which will not serve anything useful (webbug). It will send your platform/browser/and some uniquely identifyable strings to their IIS 7 webserver.
Typical tracking service. If you do not trust the client's website, do not allow scripts to execute.
As usual, if I do not find the script necessary to view the client's web content, I do not allow third party scripts to run.