Nearly any site using a web analytics package will collect browser statistics, even to the version number. Even better if you aggregate the statistics from a number of sites with different user demographics. For example, just the Apple site or the Mozilla site would give you skewed statistics. Most analytics packages will find unique users over a specified time period. Given that you use all your browsers at the participating sites, you would be counted as a unique user for all 5 browsers, distorting the statics somewhere off in the 6th or 7th decimal place.