I hiked up Harney Peak on Monday, 19 July 2010. I don't know that I have anything to add to previous reports, except that the day-use fee for Sylvan Lake is now $6.00 instead of $5.00.
After paying the day-use fee around noon I drove the short distance to the trailhead parking area and found it to be absolutely jammed. I backtracked to the parking lot in front of the store, and was fortunate to squeeze into a narrow parking space there. That added about a quarter mile to each end of the hike. Such is life in the Black Hills at the height of the tourist season.
I hit the trail around 12:15p MDT. You gain a fair amount of altitude early on, with a couple of nice views of the summit tower in the distance. Then you descend gradually for some distance before the steady climb to the summit. The trailhead sign estimated the distance at three miles, but I think it's a little more than that. About halfway there you pass into a wilderness area, which requires filling out a form and depositing it in a trailside box.
There were lots of hikers on the trail, as it was a beautiful day, mostly sunny and in the mid-70s. Ages ranged from toddlers to septuagenarians, including lots of family units. Be sure to pack plenty of fluids, as no water is available on the trail. The trail is wide and easy to follow.
I reached the summit around 2:00p MDT, and enjoyed the great view and cool breeze. There were a dozen or so other climbers there during my half hour at the top. I headed down at about 2:30p and reached the trailhead by 4:00p MDT. While at the top, clouds were forming to the north, and by the time I reached the parking lot you could hear thunder. I drove through intermittent thundershowers to Rapid City, about an hour away. So it was 3.75 hours round-trip, including half an hour at the top.
This is a nice, accessible highpoint that requires some effort, but it's not an ordeal, and well worth the time and effort. I think this was state highpoint #27 for me.