It was certainly the hike everyone says, very memorable, especially since this was my first trip to Yosemite and the first ever serious hike.
In all, you're looking at about a 20 mile day of hiking round-trip from the Valley to the top and back with an elevation gain of about 4800'. Yes, it's going to be grueling, especially during summer and if you're not in great physical shape.
The trail itself is beatiful with a mix of rocky switchbacks, excellent waterfalls, wooded areas, and then the open expanse once you gain elevation and near the dome itself.
Everyone comments about the cables and how scary it was. Funny thing, the cables to me where the best part. Yes, it is more 50 degrees steep in spots and the cable section can sometimes resemble climbing more than hiking and on either side of you there are sloping drop-offs. But, by far the most unnerving portion is the "stairs" before the cables.
When you leave the woods and start for the saddle, you will see in front of you a huge slab of granite that forms the small "bump" before Half Dome and the saddle between them.
Well, to scale this bump, you have stairs chiseled out of the rock that go up very steeply. From a distance, it looks as if people are climbing on top of each other. Also, you are by now at decent altitude of about 8,500', have been climing more than 4,000' over 8 miles, so you may very well start huffing and puffing and need to rest on the stairs frequently before making it all the way up.
Once you get on the bump, you see the saddle in front of you and that you have to decend about 20 ft and then arrive at the cables. You'll see a pile of old gloves here, tattered and full of holes. I strongly recommend that you get a $2 pair of leather garden gloves at the hardware store for this hike. This will save the skin of your hands on the cables or having to use the old gloves lying around.
On our trip, which was the last weekend before they put the cables "down", there was still many many people. Another reason why the cables were no big deal was perhaps because there was a TRAFFIC JAM on the cables! Yes, you literally had to wait and strike up conversations with others, while waiting for the line to move up/down.
Once you got up, the actual summit is very large and can fit hundreds of people. And on a busy weekend, I'm sure all that space is needed :) A well-deserved break, lunch/snacks, and viewing/snapping pictures is in order once you're here.
On the way down, if it's busy, you can go on either side of the cables, especially the right one when coming down to avoid everyone else going up/down. If you have good traction and keep your left hand on the cable, this is relatively safe, fast, and fun!
The rest of the trip down is as expected --- retrace what you've done, some slightly different perspectives, amazing parting views of Half Dome and where you've been (!), and many many switchbacks to get back to Happy Isles and the valley.
Once finished, you will be quite tired and ready for some nice rest that night. It's a memorable hike, be prepared and enjoy :)