no, I haven't ridden the Sandy Creek Trail. My brothers used to ride the Moraine Park Trail a lot, though - at the time I was staying mostly in the city (Frick Park, the cemetaries, etc) because I didn't drive and couldn't get all the way out there. (I know, I know...bike out...but I was just a kid.)
These days we've been borrowing the bikes from my husband's work - they keep 4 around for employees to use - and since he works on the North Side of Pgh, we've biked up and down that section of the Three Rivers Heritage trail. It's a nice ride up the Allegheny, but not very challenging!