I hiked the Cabin Creek Trail, Twin Pinnacles Loop and a little bit of the Appalachian Trail at Grayson Highlands State Park in southwest Virginia. All told, it was 7.1 miles with well over 1,000 feet of elevation gain (my GPS unit says 1900 but it always vastly inflates elevation gain estimates). A great park to hike in the off-season. Trip write-up to at Two-Heel Drive.
Altitude can really creep up on you if you're coming up from the flatlands. Not like the Rockies or anything, but much of the hiking is near 5,000 feet, which will be come noticeable on the uphill climbs. Signs warn to be prepared for drastic weather changes -- I would advise taking these seriously and never venturing up into the HIghlands without rain gear and your 10 Essentials.