The idea is not a new idea, in fact it is very similar to Swype. The Swype text input method holds a Guinness World Record for being fastest way to type on a touchscreen smartphone and after using it lots of people say they cannot live without it, therefore it is no real surprise to see that HTC have integrated a similar tech into the new version of Sense.
It remains to be seen if Trace will be better than Swype, the version that AndroidCentral got their hands on was very early therefore it is disabled by default, however there are options allowing you turn it on and customize the thickness of the tracing line.
The fact that this is built into Sense 3.0 suggests that it will be a feature available for all future HTC smartphones which run Android, hopefully we will come across a hands on video showing Trace in action.
Are you looking forward to using Trace in the future?