We used Diamond Gulch as our base while exploring Yosemite for 5 days.  Overall, it was a great experience with a great host!  We visited in mid to late July, so it was very hot, and this means the campground was a little dusty, but manageable.  As others have stated, there is free firewood at your site, but we were a little scared to light a wood fire given how everything was so dry.  Also, as others have mentioned the showers were great, but we did have issues with getting them to heat up.  

One thing to keep in mind is that while Groveland is only ~30 minutes from Yosemite, the drive within the park can take up 45-60 minutes.  So, plan accordingly and be prepared.  Our experience was that if we left camp around 7:30 we'd be through the gate with no line at 8am, and be at a parking lot around 9am.  This always worked for us to get a parking spot without any hassle.  After a long day of hiking and exploring the drive back to the campground felt a little long.

Something we did not expect was how little there is in Groveland itself.  We tried to spend a couple of hours there one afternoon, and ended up just grabbing coffee and going back to camp.  There just isn't much to do in town.  This isn't to discourage anyone, but keep that in mind.

The good:

* Good host

* Beautiful scenery from camp

* Clean, well serviced bathrooms (porta potties)

* Water available in camp

* Excellent showers (especially when you can get them to heat up)

* Very relaxed atmosphere

The okay:

* The sites have wood chips spread to keep down dust, but those get tracked everywhere.

* A bit of a drive from the sights in Yosemite

* On busy weekends it can get a bit crowded