The kicker, of course, is that sending video wirelessly over wi-fi or 3G/4G isn't instant, plus the utrail.me server has then got to transcode the video stream in real time and then deliver it to a friend, watching the player on their laptop or desktop. All of which means around a seventeen second delay from real time. It's unlikely that this delay is a showstopper for most users - after all, 17s is pretty close to 'live', but it's something to be aware of.
Something else to be aware of is the data used - reckon on a minimum of several megabytes of data for uploading a minute of footage on the lowest quality setting, and much more (up to 20MB/min) if your connection is fast and you set the quality higher. So watch that you don't exceed what's sensible on your data tariff.
Of course, there's the debate about whether user video needs to be strictly 'live' - sometimes taking the time to shoot video more carefully, trimming off bits and editing before uploading can pay dividends, even if it means a ten minute delay for a one minute clip. And you'll get far higher overall video and audio quality that way. Going down the 'streaming' route inevitably means bandwidth/encoding/playback compromises at every stage and quality suffers fairly horribly.
Interestingly, the developers do admit that this is only an 'initial release'. They say:
As soon as we get feedback from you, we'll roll out next update. What's possible to come: + 100% offline mode for recording (and upload when connection is available) + adapt quality to bandwidth while streaming (now one can do that manually in settings) + sharing to groups + location services support + push notifications + integration with apps
An interesting option, at the very least! You can download UTrailMe here in the Windows Phone Store.