What are yours?
Mine is most definitely dialogue. I'm terrible at it seeming natural; it always comes off as stiff and forced, at least imo. I chock that all up to being socially underdeveloped and never having really had the experiences to bounce those words off of. eh, idk, I suppose I get along fine enough. ):
I am also really bad at remembering words if it counts. I've read them, I know their definition, I know how to use them, but I never remember them when I need it. Drives me fucking crazy; combing through a thesaurus just to get a word you know already is so frustrating.

my weaknesses are... well, the same as yours, apparently. seems phony to say so, but you pretty much covered it. i hate writing dialogue, i can never put it together "naturally". and since english isn't my first language (and i write in english 99,9% of the time) i have a hard time remembering words sometimes... which is somewhat of a handicap because repetitiveness is absofuckinglutely annoying. i hate seeing one word 328443543 times on one page and it's limited how many synonyms to one word i remember :|
for example, poppy z. brite's "lost souls" had the word "purple" in it.. so.. many... times. and i wanted to stab it after few chapters (yet i still kept on reading (because of the plot)).
ugh.
uhm writing in the 'he', 'she' form
Doesn't matter to me in which language i write.
(i'm Dutch so English isn't my first language either)
Well, English is my first language, and even I have problems remembering some of the words at times. I'll have a certain description going, and I need to condense that description to one word, which just takes too much brain power for me.
Mine seems to be forgetting details that I've already said. In one chapter I may describe, say, a waterbed, but in the next couple of chapters the bed has miraculously changed into a normal bed. Also, I tend to ramble off topic for paragraphs at end. Nothing that can't be fixed with a little editing, however.
I think mine is keeping things flowing. Characters seem to either be standing around talking and thinking or racing about at breakneck speed. >:
Dialogue is tough too.
Mine are grammar mistakes specially because while I writing, I usually think in spanish :S
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...I have the word problem. xD! They are always on the tip of my tongue. I usually end up defining them to a friend (normally with what it sorta sounds like) and see if she can get it. Dx
My main problem though, is that my writing tends to get confusing. It happens when I am forming arguments too; I write what comes into my mind straight onto the paper, and that can tend to be somewhat incoherent. xD;
When I'm out of practice with words, I tend to abuse them for a month or so as well before I get the hang of them again. XD

For me, the worst part is actually finishing things that I start. I get this idea I think is awesome, write the story, and then come back later to realize that I've only written a fragment of a much longer story. And then I don't really feel up to the task of figuring out how to finish it, so I have a bunch of weird fragments just sort of hanging out. I'm thinking maybe I'll try to work them all together into one big thing someday, but who knows, they make stay fragments forever xD
I also tend to get swept up in little details. If I have an image I really want to get across exactly as I see it in my mind's eye I take as long as I feel I need to. Usually its a description of a place, so I end up getting a page of where the people are before anyone ever does anything. I guess what that really ties into is that my writing sometimes has a lot of extra fluff in it that isn't essential, but I think is fun to add in.
Overall, though, I think my biggest problem is getting started in the first place. I have flashes of inspiration that make me write for several days straight, and then I don't write anything worth reading for the next seven months or so. Sometimes I really have to force myself to write to get anything out, and then it doesn't sound as good as I'd like it to. I have a flaky muse ):<
Same here. I'm great at dialogue, but my narrative can get rather choppy.
I also have a lot of trouble getting the beginning started. Endings come easy, in fact, my endings are usually the parts I'm the most proud of, and I can also pull off solid middles, but my beginnings are always weak. In a short story, less so, but in novels my beginnings always break me. :(
I also know I skip around too much, leave out details about surroundings, and put in too many details directly relating to feelings. I figure this is bad, since you want to feel what the characters are feeling and see what's around them.
I'm pretty much the same as , only sometimes I focus on feelings too much, then later I'll focus on surroundings too much. Never do I have a good balance, unless I go over my writing a few times.
I also skip around writing scenes in weird orders, then getting confused on what goes where. @
I LOVE FIGHT SCENES FIGHT SCENES AND REALLY VULGAR SEX SCENES ARE THE ONLY THING I'M GOOD AT :(
caps necessary
i am also very bad at starting stories. it's obvious in every half-attempted story i have saved in my documents.

I must say that my biggest one is description. It's always too little, too two-dimensional, and too awkward. Second to that is not finishing what I start. I have over sixty stories. Want to know how many I've finished? Two. And the rewrites I started for those two are also unfinished.
To imagine is everything, to know is nothing at all.