We used Camp 4, 16 years ago and used it again July 2013. We love Camp 4 because it requires no reservations and it's located in Yosemite Valley. Camp 4 offers a camp site with food storages and a picnic table. It has restrooms with running water and sinks to clean up, in addition it has an area where one can fill up water for cooking or drinking. Showers are located across the street at Yosemite Lodge for $5 or use Housekeeping (located in Curry Village) for free. It's $5 per person per night to stay at Camp 4 and everyone seems to be friendly.
**Strongly recommend to arrive way before 5 A.M. to secure a camp site. We arrived at 4:15 A.M. and there were already 5 people infront of us. By 7:30 A.M. there were about 25 people behind us. Though Winter time I doubt it's busy but it's better safe than sorry**
I saw campers of all ages, families with children and it's safe. The Park Ranger Lori was informative and provided us with a map of Yosemite Village and suggested we use the free shuttle bus to get around to prevent us from being stuff in traffic. The only time we used our cars we to drive to Housekeeping for showers. Twice we walked across the street to have drinks at the bar located at the hotel. Overall it was and still is a perfect place.