[cchan]

The iPhone only samples GPS locations about 1x per second and the built-in antenna isn't the most accurate, so be aware of those limitations. Apps like Harry's give a good taste of data acquisition though, especially for the price. I have a G2X system, but if I was going the lowest cost route, that would be the one I would use.

Next step up, you can also look at the G-Tech, that looks similar in price range to the Starlane you mentioned. But it looks like you suction mount it to the windshield, which is a no-no in a lot of track groups, including BMWCCA.

Of course, if you want to spend more, it might be worth stepping up to a Traqmate or G2X system ($700-1k new).

But it all really depends on what your data collection and analysis goals are vs. cost. If you are very casual and only want to get an idea of how fast you went around a track, an iPhone app would probably do. But just a lap time won't really give you useful information about what you can improve on if that is a goal. If you are trying to analyze how well you are driving and where you can improve, I'd say that recording in-car video is a step better because it will show you what you were doing (i.e. steering inputs) and where you were on the track. Then the next step up is data aq so you can measure how much of the performance envelope (friction circle) you are using, not just a lap time.