I'm setting up Sonar Platinum on a new computer.
I purchased the Cakewalk MP3 Encoder in the hope it would be better quality and faster than LAME.
When I first tried to export to MP3, it refused to work at all until I activated the encoder.
I went to My Products page, downloaded the MP3 activation and ran it.
Then I was able to export to MP3, but the export dialog is for LAME 3.99.
 
How do I install the Cakewalk encoder?  I downloaded the MP3 Encoder again an ran it.  It looks really old. It asks what product to add MP3 to, and choices are Pro Audio 9, Home Studio, Guitar Tracks, Music Creator, Club Track, and "any other Cakewalk Product"
I chose the latter, and it says "the shared utilities folder cannot be found - Install your cakewalk application first"
 
I went through every setting category in Preferences and can't find anything regarding choosing an MP3 encoder.
Help does not describe any setting for the encoder either.
 

The integrated mp3 encoder in SONAR uses LAME. The mp3 activation process unlocks the integrated encoder. The mp3 encoder download is for much older Cakewalk products (I believe it is also based on LAME).

That seems strange. It is necessary to "activate" an open source encoder? 
I thought Cakewalk had licensed a commercial encoder, and that's why it was extra cost.  My older system still had every CW version back to PA9 on it, so it had the encoder from that I guess. 
When I built the new machine, I wanted to update to the latest encoder, and not have to keep the older PA and Sonar versions, so I bought the encoder offered with Sonar Platinum.  That seems pretty "lame" if all I got was the open-source LAME encoder.
 

Look at the External Encoder Configuration Utility on the Utilities menu. If you install LAME you can use the utility to create a new item, setting the Path and Command Line with variables as appropriate.

Lame is an open source project but as Thompson own the mp3 copyright any time a commercial use is made of an MP3 encoder, a licence fee payable. Even when the encoder is open source.

This is the case with many open source GPL licences. Free for private use not for commercial use. It's commercial because when Cakewalk add the encoder to their program it is for retail sale.

You can add the encoder yourself so there is no fee but many folks just pay the fee to have it over and done with.

I searched for higher performance MP3 encoders but don't find much of anything other than Lame. There was some work on a multi-threaded version (LAME-MT) 8-10 years ago, but apparently it was abandoned.  It's odd how much effort has gone into optimizing video encoding, but MP3 is static. I haven't benchmarked, but I suspect encoding video is now the same order of magnitude of the same speed (in terms of linear time) as MP3.
 
Still, I find it odd to encode audio for minutes watching the progress bar slowly move, while the processor utilization is 10% and the disk utilization is near zero.