WP already collects these statistics, so making them available to plugin authors shouldn't be a problem IMO.
The data would be very useful, particularly information such as what other plugins are used in conjunction with our own, plus information about the WP versions being used.
At the moment I support back a couple of point releases to make sure those running old versions don't find the plugin breaks on them, but if I knew only 0.0001% of people were running older versions then I wouldn't bother, or if the reverse were true and 10% were using very old versions then I'd be far more likely to provide support back to there.
Currently I'm just guessing stuff like this based on feedback, but it would make life a lot easier for us plugin developers if there were some sort of automated system for collecting the stats for us.
So this idea gets a big thumbs up from me :)