Anyone done it?

I sail with one, training or not. I think it can help you on the water to make adjustments, see wind shifts and help you off the water by showing your tacks/jibes,roundings. For example, I found I was constantly oversteering on port tacks. Only downside is when on the water, you can get fixated on the thing.

Any problem playing the tracks back?

No. I use that free GPSar program or the free one you get with the speed puck. I like GPSar because it has more features and you can get a data dump. No cool satellite mapping though.

What does the data dump look like? I was thinking it would be fun to write a program that can take data from a GPS and create a polar diagram from it. I've seen an app or two for iPhone that does that.

You can display your track data over map or satellite images, if that's what you mean. Sections C.2 & J in the full manual... http://gpsactionreplay.free.fr/index.php?menu=2

No, I mean what is the file format that the speedpuck spits out? Is it a csv of lat/long/time triplets, or something else?

Maybe they updated it, but when I tried the satellite overlay it was a real pain. You had to copy the map in and resize it.

I don't recall. GPSar can output a CSV I think. It's a delimited file of some sort because I opened it in Excel. I tried to write a program which would use the coordinates to identify time spent on tacks/jibs and roundings. It only worked about 70% of the time and I never took the time to work on it again.

I did do the analysis manually on 3-4 races pulling data from Kattack and figured out how much time I was taking to turn the boat versus my competitors (and how far and fast I was going on each leg). That was pretty eye opening.

Speed pucks are very cool gadgets.

Using it for training by yourself has very little value.
You have an F16 and those are very obvious when you are going faster or slower. If you had a snipe where adjustments only provided 1/100 of a knot differences instead of 3-4 then I would say a puck might have more value.

To train to race you need time on the water with other boats. Faster is usualy but not alway better if you are not going the right way. Yes you can look at some downloads and see some pointers that might indicate poor technique, but the feedback is delayed and not connected to the events going on at the time.

An hour with 2 boat training is worth 50 with just a puck, and around 52 just by yourself. IMO