Have you ever been in a meeting with your supervisor making obvious that you are completely unprepared? Today I felt horrible as I met with my supervisor and could not answer most of his questions, hadn't read my stuff, hadn't got good reasons for why I used one methodology and not another etc... it was so embarassing! I left his office so disappointed with myself... Is that what is considered to be "a low point" during a PhD? Or should I expect worse? :-)

I havent had that yet! But I suppose I would feel worse if an experiment didnt work or something like that...

I think to a degree we have all experienced things like that so don't worry. Usually it gives me the motivation to make sure that does not happen again. As long as you learn from it then try not to take it to heart too much (easier said than done I know).