What has Stephen Wolfram (founder of Mathematica) been doing after he
wrote "The New Kind of Science"? Has he achieved a following?

I can't say anything about a following, but according to a September
29, 2005, article in the NY Times, Wolfram is selling
computer-generated ring tones.

"Mathematics and music make strange bedfellows, but that didn't stop
Stephen Wolfram. Author of the computer program Mathematica and the
book "A New Kind of Science," Mr. Wolfram is now a ring tone
impresario."

"WolframTones (tones.wolfram.com) are dynamically generated ring tones
as unique as a snowflake."

The author of the article liked the ring tones, but I still prefer
human composition.

http://www.nytimes.com/2005/09/29/technology/circuits/29ring.html?ex=1133240400&en=63b6a17b1257ef4c&ei=5070

Here is a more complete answer to the second part of your question.
For the first comment, I had remembered a NY Times article and only
looked for that one. This time, I searched for recent interviews of
Stephen Wolfram. Business Week has an interview with him dated October
3, 2005.

His main effort now is towards a revised version of Mathematica. He
stated that this would be ?the biggest change since version 1.? He
himself will need the new additions to go further in the ?new kind of
science.? The article ended with what some would call hyperbole; note,
though, that the ending is not a direct quote, but the journalist?s
summary:

?He hopes to discover the program that runs the universe -- meaning
the entire universe and everything in it. He's betting it will be an
astonishingly simple program, like all the others in NKS: probably
just a handful of lines of Mathematica code.?

http://www.businessweek.com/@@jfsqloYQYMV0qhwA/magazine/content/05_40/b3953024.htm

(You may have to register at the Business Week site to see the
article, but registration is free.)

The article also lists a comment on Wolfram's book by Steven Weinberg.
This relates somewhat to the first part of your question.

Search strategy: interview ?Stephen Wolfram? and ?within 3 months? in
Google Advanced Search.

Whoever posted the last comment, I cannot thank you enought, for you
have provided me with exaclty what I was looking for! Pitty you do not
seem to be a researcher at google, as you would probably be an
excellent element.

Thanks for the kind words. You brightened my day!