i was inspired by this topic to take a closer look when mine "doesn't work". what i noticed is that the little hookie thing often ends up next to the eye instead of poking through it. i tried adjusting the needle position, but that didn't solve the problem. so now, i just manipulate the needle until i hear it snap through. it doesn't take much effort or time.
also ... since the little hookie thing is so ... well ... little ... the slightest bit of lint or other shmutz will discombobulate it, too. it pays to make sure it's completely clean.
i was prepared to do without (as i do on my other machines) if not for the earlier mention of it's value during embroidery thread changes. that little reminder got me to look closer. i'll take a closer look for the cause next time i haul out one of the others, too.
sure am glad this topic came up. :-)