Have you ever poked a microphone thinking that is was a reset/eject button (the kind that require a paper clip to be used)? Why have companies (apparently) completely overlooked the need for a label? Was it in the name of "clean" or "minimalist" design? And if that's the case... How permissible it is to jeopardize a device user experience this way?
I think it was bad design to have an unlabeled little hole that was intended to receive a metal poker. It should have been labelled with some universal symbol to indicate "it's ok to stick something in here." I guess some people are still paying the price for that old design error.
I don't think it's practical for current designers to be expected to label every little hole with "do not stick anything in this hole". The little hole that's intended to be poked is the exception and should be labelled.
Minimalist design is a part of it...or more accurately most modern devices like smartphones would be horrifically ugly and busy if every sensor were labled as such.
At a quick glance my Nexus 4 would have the following labels:
That bulleted list is hilariously long but I've left it that way since it rather reinforces my point
The fact of the matter is that most of these unlabeled features don't need labels because either the user does not directly interact with them (proximity sensors), their use is obvious after touching them (volume, power button) or their use is obvious through convention (it's a phone, so it has a speaker at the top and a mic at the bottom).
And of course there's a user's manual that explains all of these ports (which I only read to find how to eject the sim card). For something as uncommon and rarely touched by a user as a reset hole, I think requiring someone to look in the manual is a reasonable expectation. "Reset" holes are increasingly rare these days (and assorted other doodads and holes are increasingly common). If anything reset holes were a crime against usability that have taught users to cluelessly stick paperclips into random places on their device. Sometimes it's necessary to slightly confuse old, bad conventions with new products, lest design be permanently harnessed by bad designs of the past.
Newer devices tend to include longpresses/button combinations when booting/turning them off. While less standard, it doesn't require special hardware, it's discoverable when you look for it (instructions are plastered all over the internet and in the manual) and shoving random small objects into your $500 device was never a pleasant experience to begin with.
To answer your first question - No, I've never done that. Your second question assumes it was overlooked, which I don't believe it was.
To follow up what @Ben said, I don't believe the label is omitted due to clean, minimalist design necessarily. If the manufacturer expects you to poke their device with a thin metal object to reset it, or eject the DVD when the power is off, then it likely comes with a slew of instructions and/or warnings to poke the right hole and gently enough not to skewer your device. This couldn't possibly all be done by labeling the reset hole on the device and leaving the majority of users to assume you can safely poke it with a paperclip because they were instructed to do that on a different device.
By not labeling it, you are assisting the user in finding out the right information on how to reset this device, including the labeling of which hole to stick your paperclip in, lest you risk damaging it, if that is indeed the prescribed method. This isn't an open pass to jam a paperclip into 'unknown hole at the top' hoping that will reset your device. I also don't believe the manufacturer has jeopardized the usability of the device because some other manufacturer thought that was an acceptable solution for reset or that's where the reset hole was located on a different device.
Just curious - the first time you ever had to reset using a paperclip, how did you figure out how to do it? I learned how to eject my SIM card from something like this which has very clear labels: http://support.apple.com/kb/HT5163