Thanks for that great explanation -- (my interest in in man-machine
interfaces has always made this an interesting topic for me).

I've got to say, I totally get you.  I know exactly how you feel
because its exactly how I feel about "Auto Indent".  I drives me nuts
in exactly the ways you've described about Auto Enclose, and for the
same exact reasons.  It totally intrudes on my typing, disrupting my
train of thought because its guessing wrong half the time and forcing
me into a bunch of little "decisions" whether I need to press Tab or
Backspace.  I know what I want to type, I just want to let-it-flow.

This made me pause to ask, "so why do I like Auto Enclose so much, but
not Auto Indent?"

It's because of Squeak's amazing little collection of 2 or 3 editing
features turn it into like a poor-mans Scratch.  You know, the ones
we've been talking about:  1) selecting innards, 2) hot-key
adding/removing of surrounding enclosures, 3) auto format.  Once using
those, Auto Enclose rounds it out nicely, (and disabling
selectionMayShrink boosts it even one more notch).

>> You know, I bet this boils down to a simple cost-benefit analysis. For me,
>> the effort required to
>> type a character at the cursor position is negligible, so saving that
>> effort is of little benefit. Even
>> in cases where I will need to put a $) after the expression I'm typing
>> now, sometimes I'll have to
>> type right-arrow to get past it. So the benefit is very small and often
>> offset by a small loss.

It's not about saving keystrokes.  It's about automatic closure of
multiple nested expressions.  Query's like this are almost impossible
to "type" without Auto Enclose:

     ^ (cube
          plot: [ : dim | dim date month ]
          measures:
               [ : meas |
               (meas mean score plotNumber: 1)
               , ((meas
                    define: #fractionOfWinners
                    as: [ : cell | cell total winnerCount / cell total
count ]) plotNumber: 2)
               , (meas mean gainFactor
                    plotNumber: 3;
                    colorizer: [ : val | val > 0 ifTrue: [Color green
twiceDarker] ifFalse: [ Color red twiceDarker ] ]) ]
          where:
               [ : cell |
               (cell dimension date year equalTo: Date today asYear)
               | (cell dimension date year equalTo: Date today asYear
previous) ]) open

It'd be much more easily "assembled", expression by expression, but
Auto Enclose gives typing it at least a chance of success.  :)

>> Similarly, deleting an unwanted character is cheap, but deciding whether
>> to do so is a huge cost.
>> I have to stop thinking about what I'm doing, and think ahead to what I'm
>> going to do next. Even
>> if I know I'm going to need the closing character, it stays in my field of
>> view and takes up cycles
>> as a pending thing that I have to worry about until I complete the encoded
>> expression.

So I'm surprised you don't better appreciate the atomicity of
expression-editing.  Deleting a paren/brace/quote character breaks the
code and even breaks the formatter so you can get really stuck on
complex expressions.  Taking an approach of expression-editing, one is
determined not to let the code ever be broken even for a short period
of time.

>> So, the benefit is small and unreliable, while the cost is large and
>> inevitable. It forces me to think
>> about typing, which normally I don't have to do. Thus, it's infuriating.

Yep, I totally get you.  But if you ever decide to try committing to
Squeak's very capable expression-editing functions, I hope it'll work
out as well for you as for me.