Yosemite Wilderness Conditions are available here:
http://www.nps.gov/yose/planyourvisit/wildcond.htm
Here's the status as of today (May 12, 2010):
The Half Dome cables will not be in place over the May 21-23 permit period. Snowpack in the Yosemite high country is currently well above average (134% in the Merced River basin), with the potential for additional cool, wet weather in the next week. As a result, the Half Dome cable route and subdome are covered in deep snow, making trail conditions poor. For the safety of National Park Service employees setting up the cables and for hikers, the cables will not be put up until conditions improve. We will monitor conditions over the next two weeks and issue an expected opening date as soon as possible. If you have a permit for May 21-23, you will receive a refund for the reservation fee. (Learn more about the Half Dome hike. Please note that permits are required to hike to Half Dome on Fridays-Sundays and holidays beginning this year.)
The Mist Trail from near Vernal Fall Footbridge to the top of Vernal Fall (and to Nevada Fall) is open. The John Muir Trail between Clark Point and the Panorama Trail (near the top of Nevada Fall) is closed for the season.
The Four Mile Trail to Glacier Point is closed for the season at Union Point (no access to Glacier Point).
The southern portion of the Mirror Lake Loop is closed due to a rock fall. (Access to Mirror Lake and Snow Creek Trail is still available, as usual.)
The trail to Wapama Falls is closed to stock (but is open to hikers) beyond the Beehive junction due to a rock fall.