Yeah, UTM will provide you with a fairly accurate unique and repeat count. Problem is ... your log file will be huge. We had to turn it off on several large sites as it got out of hand -- 2GB per day and was taking a toll on the server.
UTM does generate huge log files, but disk space is cheap these days. You lose a huge amount of useful information if you don't use it.
For one site, we've recently started using Google Analytics (formerly Urchin's ASP version), which gives much, much better stats. Unfortunately, it can sometimes slow down page loading, so we've been careful about using it on more highly trafficked sites.