typewriter!
Also at 10 letters pepperwort, prerequire, pretorture, proprietor, and repertoire.
And you can spell ‘stewardess’ using only the letters from the left side of the keyboard!
dan: you can get two more letters (and fire up lesbian porn fantasies) by writing STEWARDESSES. The fact that you need only one hand is a fringe benefit.
Submitted for your perusal: A Collection of Word Oddities and Trivia concurs with KidCharlemagne on his TYPEWRITER comment, but also suggests the nonstandard TEETERTOTTER (it’s normally hyphenated) as an alternate.
Incidentally, AFTERCATARACTS (plural for a condition that sometimes follows cataract surgery), TESSERADECADES and TETRASTEARATES are the longest words which can be typed using only the fingers of the left hand.
How about the right side of the keyboard?
::hmm:: opinion…minion…monopoly…
and I thought i was the only freak.
You’ve been here over a year and you still thought you were the only freak?
Have you been hiding in the ATMB forum or what? 
What, you mean qwertyuiop is not a word?
How 'bout “powertripper” is that a word? If not, it is now. 12 letters…hot damn…I’m THE MAN. Now go get me a beer.
What do either of the latter 2 words mean?
actually…
its:
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE…P!
Man that was freaky! All of you replyers had posted between the time I read the OP and finished posting!
Coincidentally, this is also the longest word that can be spelled using only the letter E.
I always found typing “pleasing” to be pleasing.
::Whistles innocently and then stops.::
Oh, wait…it looks like I dropped my bag of nice rupturewort. Which, incidentally, has 11 letters. I wonder if that has anything to do with the top row of a normal QWERTY keyboard?
::And then runs like hell!::
Maybe not the longest, but that certainly is an interesting word.
[Mini-Slight-Not So Much-Kinda Not At All–Hijack]
It is an interesting word…except, what’s the point of it? I mean, why torture someone before you go an torture him? According to this reference it means to torture beforehand. Before what? More torture? How can you torture before you torture? Just curious, ya’ know, 'cause I got me here some black leather gloves, and a rack…and I wanna get started soon.
[/Mini-Slight-Not So Much-Kinda Not At All–Hijack]
I got some for ya:
UTOPIERITY (n): 1. A made up word, defining the possessive state of being in a veritable utopia. Note, we said veritable utopia.
TURTIQUE 1. (n) Another made up word defining an early art form of primitive Rennaissance cultures relating to the turtle or tortoise. 2. (adj) Something slow and obtuse.
QUEUEPETIQUE 1. (adj) Yet a tertiary made up word, describing a line of people that may seem like a queue, but really isn’t.
Tripler
Trust me on these, they exist in my vocabulary.
Huh. I’ve only got function keys on the top row of my keyboard. I can’t spell a damn thing with them.