I bought the iSmartTrain software from OTAG on 2005-10-12 for use with my Polar S625X heart rate monitor, and I've been happily using it ever since. The Polar Precision Performance Software™ included with the HRM is OK software, but running it on Windows in a Virtual PC on a Mac just feels sluggish and perverted. Since iSmartTrain is a native application on Mac (Linux and Windows too) it is much faster and better looking.
After having bought a Polar serial IR interface and a Keyspan USA-19HS serial/USB adapter everything worked. The direct Polar IR-USB connector doesn't work because it's not USB1.1 compliant according to the FAQ, and the Keyspan serial adapter is the one they recommend, and eXpansys had them at a fair price (they shipped it from Manchester, UK, and it was delivered to me in Denmark the day after!).
The import of data is a little cumbersome as I have to initiate it from my HRM, it doesn't initiate it automatically from the computer like it does with the PPP software. Apart from that it just works, the data is imported and you can write a log message for detailing the workout and some notes, much better than the PPP software which only allow an inadequate size for comments, 200 characters or so. I often need more.
The calendar view of the training log is great, you get a very good overview and you can read the log messages in the same view by clicking on a session. What it is lacking is a general diary where you can enter daily statistics like resting heartrate, weight, amount of sleep and a short comment every day. A planning feature with graphs so you can see how well you're following your plan would be extremely cool too. These wishes and many more have been put forth on the forum in a thread where the lead developer solicits wishlist items for the next major release.
If they would, and could, add support for the cycling specific and power based Normalized power, Intensity Factor (if), and Training Stress Score (TSS) as implemented in CyclingPeaks it would be truly grand. It does look like the formulas for calculating TSS and IF are proprietary though, and I can understand if CyclingPeaks and Andrew Coggan, the inventor and power training guru, want to keep it to themselves.
I can certainly recommend this software, getting rid of the dependency on the POS Virtual PC is, is a relief, and I like the fact that the lead developer is as responsive as he is, there's both a forum that he moderates and a developer blog, much more than I would expect in this kind of software.