The intention is to solve for the causal user who isn't putting in their own expressions, they're just picking from the pulldown - to have the out of the box behavior "just work" for everyone. With the existing behavior, you either a. have the mrulist turned off, and then have to either scroll down a bunch/weed through the default options, or b. have your MRUs, but not have a reference for what other possible/typical expressions there are. For what I'm doing, there's a couple (hence the default of 5) of maximizers I use repeatedly, and having them appear at the top of the list makes that much more accessible for me (and hopefully everyone else) - but I still want to see all the other default options..
- the separator, shrug. easy enough to kill - I didn't like the way it looked without it, because the list "ran together" and it wasn't obvious when the mru choices ended and the default list stopped... but please, we can easily drop that from the patch, that's not core to the "point".
- the issues with bad default items, I agree with - but I don't think the fix is to not have them there, the fix is to get better defaults.

If you've got a cutlist of ones you'd want me to improve, please share and I'll take a stab a it.
- For your additional solutions, I think the first solution is very similar to what I did? Is it because I also included the defaults that you don't feel it fits?
- for the second solution, I felt that adding add/remove/etc buttons to "manage" the list would get too messy, too quickly - which is part of why I suspect you didn't go that route...

I dislike UI that forces users to micromanage the details, and would prefer to work towards a list of expressions that just works as much as possible.
- for the third, that seems like an additional patch that's in addition to this, to add a section to the "help" text that explains all the defaults and what they do. Sound good? If so, I'll whip up something.