I've been playing with Google Analytics since I saw Tim Bray mention it last week. It looks like Google bought the Urchin webserver stats cruncher, rolled into their Adsense service, and are offering it for free. Although it seems rather tilted towards optimizing Adsense revenue, it's also quite useful for non-Adsense usage.
I've been letting it chew for a week to see what kind of data it came up with, and am really impressed with the reports it provides. My only real beefs are that the data is delayed (-1/2 star) - by sometimes a day or more - and that it borks in Safari (-1/2 star). And, the interface seems really complicated (-1 star) - I keep forgetting where the various reports live. Are they visible under "Executive" mode? "Webmaster"? "Marketer"? And, some of the terminology used to describe the reports is a bit non-intuitive. Maybe not if you're an Adsense geek, but for a regular web-head, I keep thinking "uh, what does this report tell me - they do provide nice paragraphs under each report to give the gist of it, though.
The report delay is really noticeable because I'm also using Sitemeter, which provides up-to-the-second reporting. That's how I saw the traffic spike sent from TUAW this morning. I would have completely missed that (until it was over) if I was relying on the Analytics reports.
The reports are displayed in dynamic form - either "ajax" (blech) or Flash, depending on the report, making drilling down into the data a bit less unpleasant. I personally love the "Map Overlay" view, showing where the last 50/100/500 viewers were from. I wish there was a way to teleport to the other end of a network connection. There are several blog readers in locations I'd love to visit :-)
The other really cool report matches entry pages with exit pages, so you can see sort of a flow through the data on the blog. Very cool, seeing how people are taking advantage of the alternative navigation links (related entries, calendars, tabs, searches).
It doesn't have a way to track RSS traffic. If it did, I'd gleefully bump the review up to 5 stars, and ignore the no-Safari display. I can live with a few hours of delay on the reports, too.