I don't think there is a semantic difference, since I would probably transcribe what pg said he said as "ineffectual, perpetual grad student." Note the comma, which implies an "and" relationship between adjectives.

I believe gparent was pointing out that the phrase "ineffectual and perpetual grad student", nuance aside, literally means the same thing as "ineffectual perpetual grad student".

In my mind inserting the 'and' separates the 'ineffectual' and 'perpetual' so it appears the person being described could be a perpetual grad student as an independent idea -- but maybe they just love school life, so it's not really anything negative. Leaving the 'and' out, however, implies to me the person is probably a perpetual grad student because of being ineffectual.

Exactly what I'm thinking. If you remove the and there are two interpretations ( blame english for this). both ineffectual and perpetual or just perpetual or just ineffectual.

Yes, unfortunately no language is an optimum form of communication, so we rely on other cues (often body language when available) to try to determine what an author/speaker really means to convey. Word choice does play a role in that, which is why I think pg (or anybody) would prefer to be quoted correctly :)