I think what I'm saying is more important to the type of interviews you do. And I think for the most part we agree (or I misunderstand?). Those interviews sound much closer to the classic engineering interview (as in not programming but like mechanical or civil engineering) or typical science interview. I think those are better interviews and more meaningful than live coding sessions or whiteboard problems.

Maybe here's a general question you can add (if you don't already use it) to bring out that thinking even if they're nervous. Since it's systems they are familiar with (my forum entry example is similar. I don't do front end), ask them what things they're frustrated with in tools they've used and how they could be fixed. It can help to ask if they've tried different solutions. With email that can be like if they just use Gmail via the Web, just use outlook or Apple Mail, or have tried things like Thunderbird, mux, or other aggregators. Why do they like the one they use? And if they've tried others I think that in itself is a signal that they will look for improvements on their own.

The things I think many interviews do poorly at is that they tend to look for knowledge. I get this, it's the easiest thing to measure because it's tangible. It's something you "have". While this matters, the job is often more dependent on intelligence and wisdom which are more about inference, attention, flexibility, and extrapolation. So I don't think it's so much about "gotchas" -- especially as many now just measure how "prepared" they are -- but, like you said, the way they think.

I'd much rather take someone with less knowledge (within reason) who is more intelligent, curious, and/or self driven by the work (not external things like money or prestige). Especially with juniors. A junior is an investment and thus more about their potential. As they say, you cannot teach someone who "already knows".

[EDIT]:

There's something else I should bring up about the "classic engineering" interview. Often they will discuss a problem they are actively working on. A reason for this is 1) it is fresh in their mind, 2) it gets at details, *but* 3) because it makes it easier for the interviewee to say "I don't know."

I think this is often an issue and sometimes why people will say weird erroneous things. They feel pressured to not admit they don't know and under those conditions, a guess is probably a better strategy. Since admitting lack of knowledge is an automatic "failure" while a guess has some chance, even if very small. At least some will admit to guessing before they do and you can also say its fine to guess and I see that often relax people and frequently results in them not guessing and instead reason through it (usually out loud).

(I'm an older grad student finishing up, so I frequently am dealing with undergrads where I'm teaching a class, holding office hours, or mentoring them in the lab. I've done interviews when I was a full time employee before grad school, and I notice there's a lot of similarities in these situations. That people are afraid to admit lack of knowledge when there is an "expert" in front of them. Even if they are explicitly there to get knowledge from said expert.)