I tried posting once but it looks like it didn't work so here goes again.
My sister and I did this trail on a bright, sunny day. It took us two old gals about five and a half hours, including stops for lunch, nature admiration, and photography. We found it simply glorious. It starts on the Sugarloaf State Park side in a lovely little redwood grove that runs along a babbling brook, then rises into grassland, then up into oak/madrone forest, and out along a ridge that takes you to the final little uphill push to Gunsight Rock. Fabulous views from the grasslands up, all along the trail. Indian warrior in full bloom at Gunsight Rock; manzanita groves blooming pretty much all along the trail.
The view from Gunsight Rock, of course, is legendary - all of Sonoma Valley from Oakmont down to the Bay, with Mt. Tam, Mt. Diablo, and the towers of San Francisco visible in the distant haze.
The trail is very well maintained on the SugarLoaf State Park side; somewhat rougher after it crosses into Hood Mountain Regional Park but still quite good. The trail is well graded and presents no difficulty to reasonably fit, experienced hikers. The only tricky spot was fording Sonoma Creek. In early March the water was deep and fast flowing, but we managed to rock hop across. I chose to get my boots a bit wet in spots rather than risk balancing on a wet pointed rock, my theory being that I prefer a wet foot to a broken back, however I didn't get any real soakers. Later in the season as the flow slows down to a trickle this shouldn't be an issue.
Beautiful hike; highly recommended. Walking stick came in handy fording the creek.