Yes (emphatically) and No (doubtfully).
Unless you are creating some manner of internal tool for a group where you know IE6 penetration (no pun intended) is high; ignore IE6. With vigor.
As for IE7, it's a bit of a toss-up. Generally speaking, if you are aiming for the private sector, you can get away with ignoring it (for the most part) and assuming that your IE8 support will take care of the most heinous problems; but if it's a site for selling stuff (specifically a web-shop; sales pitch site, etc.), you might want to at least check that it looks somewhat sane, and add a few small fixes as appropriate.
As an aside; and a real-world example; at my site of employment (we do web sites) we are currently undergoing (or rather, considering) a shift vis-a-vis IE-support in general: Prices are stated with basic IE8 support; full IE8 support would cost ~10% more; IE7 ~30% more and IE6 support ~100% more.
Edit: Think of it as charging extra to make a camper wagon designed for a WV to work with, respectively, a pinto, a yugo and a horse-drawn carriage.
