Butte camp trail was fanastic. Take a walk through the dry pine forests on the south side of Mount St. Helens. The trail is well kept and fairly easy. Most of the undergrowth consists of Lupins and saplings coming through a carpet of dry moss. Be prepared to enjoy these forest views, you'll only see the mountain at the beginning and the end of the trail (ok maybe you'll catch a view through the trees).
Make sure to bring your bug protector. Not bad for mosquitos. However, the biting flies were out in force. If you are camping at Butte camp I recommend staying to the right side of the trail. The left side is bumpy and full of mosquitos.
Once you get past Just beyond Butte camp, on the way towards the Loowit trail, there are some downed trees across the trail. If you are carrying a pack this will slow you down a bit. I counted 5 spots where it was necessary to leave the trail to get around the trees.
Don't let this discourage you, the payoff at the top is fantastic. You'll enjoy a great view of mount hood, mount adams, and of Course Mt. St. Helens. The upper part of the trail is packed with wild flowers. Make sure you bring water with you. there are some patches of snow off of the trail, that can be melted, but little in the way of an accessible water source.
If you are headed to butte camp trail you may also want to check out the Ape Caves.