You can read about it here: http://www.voipbloggen.dk/woopra-trafikanalyse-afmystificeret It's in danish, but to sum up:
I love it for a number of reasons, but mainly because it demystifies web analytics, showing people instead of trends.
I fear it because it shows faces behind cold numbers, and gives Woopra the possibility to put faces to IP's. Although their/your :-) privacy policy looks very humane: http://www.woopra.com/privacy