I get sick of all the ACID, ACID, ACID clammoring. A benchmark, not a priority -- and by no means the true measure of a browser--not yet, anyway.
I have mixed feelings on Acid2 myself. Yes, it has been misrepresented in what it is supposed to achieve, and supporting it will not make cross-browser dev headaches go away completely. But
it really does test a series a fundamental building blocks that have never been properly addressed. Of course web devs have been hacking round browser bugs since the WWW was born. The IE 7 team has tried to fix all the glaring bugs in existing things it breaks (which is good), and simply cannot address the changes Acid2 requires. Neither can Mozilla till the gecko core gets a serious reworking. It took Opera a year to implement its fixes.
Though the test itself looks "dumb", the techniques behind it aren't - solid positioning, min/max-width/height, generated content, CSS tables and others would make a clear difference in what web developers can achieve, and what users would experience. That is important for accesibility and many other things...
 I DO welcome IE7 - anything that is less of a buggy mess that IE6 was is warmly greeted!