In the new forum, how do I keep track of which questions I've read and which ones I haven't.

This isn't really an "answer", but rather more of a workaround until there is a good answer.
I'm trying out adding interesting categories to my "favorites" list.  Whenever there is a question/answer in that category, it shows up as email, and then I can just use my email client as my forum reader.  If I want to comment/answer, I would then click on the link in the email.
Advantage: Forum entries accumulate in my email inbox for accessing while off-line (e.g. when traveling).
Disadvantage: Does not provide a good way to occasionally scan non-favorite items, since they end up mixed up with the ones on my favorites list that I've already read through email.

no thanks.. don't need email for every update..

how do I see who posted last?  I look in for activity, and see questions I posted to (both answers and new questions).
if I am the last poster, then there is no need to look again..   response times vary from a day or longer..  opening every topic again is a waste of time.

Regarding the questions you haven't read, I'll see if we can add a different color for visited links.  In addition, we have some ideas for a future enhancement to add a view where you would be able to see an activity feed with incoming answers.