Five days in and no krausen!! The airlock is bubbling like crazy but no krausen has formed after five days. For the first two days there was a thick foamy raft floating over my noob concoction but on the third day it subsided and now only smatterings of what I assume to be yeasty debris of some sort remains. Is this normal? Am I making the classic rookie mistake of worrying unnecessarily? Should I pitch more yeast? I did brew from an extract kit and read in a couple places that sometimes the yeast in kits is old. Any guidance is welcome.
You said that "For the first two days there was a thick foamy raft floating over" your brew. That sounds like krausen to me! Do a quick search for "krausen" on Google images and you will see lots of results that look just like your brew did a couple days ago. The yeast are most active for only a couple days. There will be some lag before they start, then they get real busy before finally settling down at the bottom of your fermenter.
To answer your questions directly: Yes, it sounds very normal! Yes, this is a classic case of unnecessary worrying. No, don't pitch more yeast.
"Relax. Don't worry. And have a homebrew."
A very simple way to tell is this:
If you see bubbles, then your yeast is doing its job. If you do not see any bubbles, then your yeast is dead. You should expect a new bubble every second in the first few days, and going down to a new bubble as the fermentation process continues. If you do not see a bubble within sixty seconds, then your yeast is dead or the fermentation process is probably complete.
If your yeast is dead, I would recommend pitching more yeast and shake vigorously to activate the yeast. Do not worry about pitching too much yeast just yet; it's not about perfection, it's more about having a successful batch! I would worry more about the common case: inactive (dead) yeast, or not enough yeast. I use liquid yeast exclusively now because I have had troubles activating the from a dry form in the past, and have always had success with liquid yeast.
Keep in mind the purpose of the yeast. The purpose of the yeast in the fermentation process is to take the sugars that existed from the wort, and metabolize the sugar in the sweet wort into alcohol. The yeast will thrive on the sugar, multiply, and chew up all of the sugars that exist inside of your beer. If there is no sugar left, then the yeast will die and end in the bottom of the carboy in the trub. Pitching more yeast will change the recipe a bit, but in the end you just will have more in your trub.