Yeah, sounds like your experience was similar to mine. Up to 2006 I got CONSISTENTLY STUNNING results using ACAD's internal renderer and its internal material library which I routinely tweaked to create new custom materials, from various polished or brushed metals to stonework, green marble, gold, etc, to water and sky. I was COMPLETELY SOLD on ACAd's included internal renderer. It even included time- season and LONG/LAT controls for lighting if you wanted ! This was HUGELY useful when I was modeling Swimming pools and inserting perspective renders (including water features and ALL !!!!) into photographs of customers' homes with back yards and existing or subsequent landscaping... I'm sure you can see why I was SUCH a fan ! I also had huge successes with it modeling Mechanical Industrial and Consumer products, INCLUDING steel, copper, gold, black and colored rubber, colored plastics AND transparent materials... !
And imagine the value of running ACAD-2006 on a machine not far removed from today's available equipment ! Relatively low software "weight" on a fairy robust platform even by today's standards. AUTOCAD NIRVANNA (almost !)
Then came the "Improvements". I abandoned ACAD with 2008, and have only used it under duress since. ACAD 2010 saw some significant return to sanity, with more improvements at 2011, but they're still struggling (monster sized legacy icons anyone ?!???). I expect 2012 (out now) and further releases to make things better. Who knows- maybe in a another few releases we'll be up to where we were before the improvements of 2008 !
BTW- I long ago replaced the included PDF generator with PDF995. Superior and far more consistent results. AND there are others out there that may be even better !
I'd SERIOUSLY look into anti-aliasing settings and screen-capture as a port-out for your work. You can take the results out to any bitmap editor, tweak the results as you see fit, insert the resulting image ino ANY page manager (I us MS-WORD for consistency and broad compatibility purposes) and THEN output to PDF. Seems like an extra step or 2 but that impression is FALSE, especially when compared to the VERY REAL circumstance prompting the initial post in the first place !
Good luck and post back here with results -
C.F.