I'm starting to get a handle on it, and I find it cumbersome that you can't have the current theme open that you want to edit.  So you are constantly switching to some other theme, so you edit the them you want..... then switch back and see your changes.  Lots of mouse clicking.
 
That said, seems I make changes and many times they don't show.  But, I'm not sure.  First of all, figuring out what item you're changing sometimes is a total guess.  So I'll make a HUGE adjustment.... like make the item/background.... whatever... some color like bright red, so it will be obvious what it is.  I'll do that and nothing happens.
 
Also it seems like some items I'm diverted to my editor and some items I can edit within the theme editor.  ...or both.  It's really confusing.

In the end, if it was easy to know WHAT ITEM you were editing, that would be sweet.  Yeah...some are obvious like the meters and such...  but the "important" stuff like backgrounds, clip backgrounds, etc...  That's what I can't get 100%
Where's the comprehensive tutorial??
 

You should be able to open multiple themes at once...that makes life really easy when you want to copy attributes from one theme to another. However remember the Theme Editor is a separate program, so you need to open up two instances to do this.

Having multiple editors open I suppose could be handy if you're wanting something in one theme. to put in another.
 
My issues are figuring out WHAT is the item that I want to edit.  I've looked at some themes that are different to try and help my searching (and used bold colors to maybe make THAT items stand out), but like mentioned, sometimes the "edit" doesn't seem to always work....or I'm on the wrong "item".   Hence asking if there have been any "issues" other people have noticed.
 
The 2nd issue is that I can't have Sonar running a theme, that I want to edit, so I can instantly see how the edit looks.  If the OPEN Sonar theme automatically updated as you edit, that would be sweet.   I'm finding it sometimes takes several tweaks on a color, to get it desirable.  I've started out with some real train wrecks, but after several tweaks on a background color for instance, you finally get there.  Having Sonar OPEN with that theme to immediately see finished edits would be nice.

Lastly... I'm digging the editor, but it's tedious to say the least.  Also, I'm "guessing" at what color shade or hue I want, as I have NO idea how it will blend with the rest of the theme, until I look at it as a whole.
 
thx Craig for your reply.   I think I've got a real good theme happening that offers more contrast than Mercury, but is still "gentle" on the eyes, like Mercury is. 
 
I find things like grey text changed to black makes a big difference and lighter text backgrounds for instance.  Heavy handed colors are nice, but to me become a bit of a distraction and aren't really helpful, as there are too many colors.  Mercury is at the top of my list...I know not for others though.  Tungston is soooo dark.

There's no question that a) designing a really good theme is not for the faint of heart, b) Cakewalk does have improvements they'd like to make, c) it's indeed difficult to figure out how to change some elements (and some can't be changed), but also, d) it's fairly easy to make relatively small, but helpful tweaks.
 
I'll be interested to see what you come up with, and hope you contribute it to the user theme collection!

Some time back, a forum member posted screenshots that highlighted the areas of the interface with the related elements from the theme editor marked on it. I think that's what the OP is looking for. I can't find them, but a review of the theme editor threads may point the way.
It's something I would use if I was going to create a theme.

Like you, that may have been something they were wishing foralso. Such a thing would be a huge undertaking for anyone to accomplish.