I use this trail very often to bike commute between my house in Port Matilda and State College. I ride the whole existing length from the McKee Street/Clinton Avenue Bike Path to Montauk Circle, which includes both the improved and unimproved sections.
The improved section from the McKee Street/Clinton Avenue Bike Path to the Toftrees property just beyond the I-99 overpass is very nice, generally well-maintained, and easy riding on a smooth, even surface (I currently commute on a road-touring bike with 35c tires). This section, however is just over a mile long and not very useful for getting anywhere by itself.
The remainder of the existing trail is unimproved and mostly unmaintained. The surface is rocky and rough in many spots to the point where if it were any rougher, it would be unsuitable for my touring bike. The trail is perfectly fine for a wider-tired bike for its entire length. Through the unimproved section, there are a few muddy spots with poor drainage, and there are a few spots that get washed out pretty badly in heavy rain. The at-grade crossing of Toftrees Ave. can be a pain, especially at rush-hour. Currently (12-12-2012) there is construction going on above the trail near Toftrees, and construction vehicles have been using the trail, so it is rougher and muddier than usual.
Hopefully improvement and extension of this trail continues in the future, as even a small amount of improvement would have tremendous benefit for a large number of potential commuters.