Wow! What a fantastic overnighter! Someone else described this hike as a "Four booter for sure" - referring to the Copelands' hike rating system - and they're absolutely right. Once above the treeline (which takes less than 2 hours) it's views, views, views all the way. The Iceline views are fantastic enough with glaciers to your left and Takakkaw Falls and the Daly glacier across the valley to your right, but I personally think that the view from the Whaleback is even better as you get to look back (south) on the Iceline, and have clear views to Mt Des Poilus and several glaciers to the north. Lots of running creeks to get water and numerous spectacular waterfalls.
Note that the trip is very asymmetric: day 1 is only 11 km, though with most of the elevation gain (700 m), while day 2 is 18 km with about 300 m of (steep!) elevation gain. However, on the first day along the Iceline trail, there are lots of little ups and downs over moraines which probably add another 100-200 m all told (not included in the stats of the hike). The last 8 km or so of the hike are down in the valley with no views, and they kinda drag, but your pack is at its lightest and it's time to step out and knock off those km. The trail is well-defined, easy to follow and in good shape but don't do what we did and get distracted by the Twin Falls chalet to continue over the bridge down to Marpole Lake... By all means investigate the chalet (they serve snacks when open) but return to the trail junction and continue down into the valley.
I agree completely with the Copelands' direction of starting with the Iceline first, then the Whaleback so you are not hiking (and therefore squinting) into the sun.
We camped at Little Yoho Valley backcountry campground. We picked up our annual parks pass and paid for the camping at the visitor centre in Field. Parks Canada insists on booking backcountry campsites, though the campgrounds seem to be kinda ad-hoc in terms of tent placement. Any old flat spot will do and there seems to be more space than Parks Canada would have you believe. There is a pleasant designated eating area with picnic tables (which seems a little close to the tents for my liking) and a tall pole for food storage. Unfortunately the composting outhouse has a serious infestation issue right now (maggots all over the seat X-P) and we were disgusted to find piles of toilet paper all through the trees up the hill behind the outhouse. Come on people, the very least you could do is throw the TP into the toilet :-( Fortunately the very nice people at the nearby ACC Stanley Hut let us use their exemplary facilities. Upstream from the campground a narrow trail leads to a lovely little double waterfall. Outhouse issues aside, the campground is in a gorgeous spot.
Takakkaw Falls campground is gorgeous though, and is clean and well maintained as it is officially a frontcountry campground (despite having to walk in). We bagged a great site with a view of the falls as we walked back into the campground :-) Landing there mid-week meant we had no problem getting a site.
Yoho is truly a spectacular park - this trip is highly recommended.
Photos are here:
Misc Yoho: http://www.flickr.com/photos/mkandag/sets/72157628638690019/
Iceline: http://www.flickr.com/photos/mkandag/sets/72157628638690019/
Whaleback: http://www.flickr.com/photos/mkandag/sets/72157628200173615/