From browsing around my account, there's now an activation tab and it looks like the new Sonar is going to be a challenge-response activation limited to a specific machine.  Is that correct?  Do we know how many machines?  With limited exceptions for special software I use only occasionally, I do not buy any challenge-response software, so this will probably be the end of the road for me for Sonar if this is true.  Bought every version since 3.0, but I won't continue if this is the case.
 

Not limited to one or any number of machines, but of course they would frown upon and get suspicious over someone having 100 installations with only one licence. I think it was Noel who said this in an earlier post.

Cakewalk had and still does have one of the most flexible activation methods. Although I can't imagine what software you could possibly own if you don't even accept challenge response as a security precaution.

Ric4001
From browsing around my account, there's now an activation tab and it looks like the new Sonar is going to be a challenge-response activation limited to a specific machine.  Is that correct?  Do we know how many machines?  With limited exceptions for special software I use only occasionally, I do not buy any challenge-response software, so this will probably be the end of the road for me for Sonar if this is true.  Bought every version since 3.0, but I won't continue if this is the case.
 

What do you think the current system uses, if not challenge & response?
 
Every time you input a serial number you're doing exactly this!

see Noel's comments about installing on multiple machines here http://forum.cakewalk.com/FindPost/3145016

Thanks for the link to the other thread.  Being able to install on multiple machines is my concern, and Noel's comment eliminates my concern. 
 
For Bristol: there's a big difference between serial #s and challenge-response.  Serials are not tied to a specific machine; challenge-response is.

Bristol_Jonesey
 
What do you think the current system uses, if not challenge & response?
 
Every time you input a serial number you're doing exactly this!

The confusion may be over what the term "challenge & response" means. In its broadest sense BJ is correct, a password or serial number system qualifies as challenge and response authentication. The software asks you for your serial number, you respond with your serial number and an activity occurs as a result of your correct answer. But it is also a term used by some software vendors to describe a more restrictive system in which a hash is generated of your individual computer components which is then exchanged with the authentication server and locked into the account to prevent the software from being used on another machine.