I thought it was only the frontpage. Just checked my wishlist and every single thing is on sale
pretty much every game on Steam has some sort of discount for the sale. but you should wait to see if they become 'daily deals' and get discounted more. the general rule with Steam sales is only buy 'daily deals' (or 'flash/community-choice', but those aren't part of this sale) or wait to the last day. otherwise you might get it now for 40% off, but then it's like 75% off tomorrow
but if it's already 75+% off, it probably won't be cheaper, and you might as well jump on it
edit: and this sale is a little different from previous sales. basically every day (at 12pm PST) we get two sets of 'daily deals': the top set lasts 48hrs, and the bottom set lasts 24 hours. but to be clear, we get two new sets every day, so the previous day's 48hr deals are still active, but no longer on the front page