Hi there! Wanted to share my experience with TOEFL exam, got scores today 113: R29 L30 S27 W 27
I know English pretty well, though I've never lived in english speaking country. I read most of the time in english, watch movies in original etc. First I downloaded sample test from ETS got everything right on reading and listening so I decided to schedule my exam right away. I had a week left so I prepared quite a bit:

After registration for exam you'll be provided another sample test so please do it! pay attention to speaking and writing samples they provide
I also watched notefull videos on youtube - they are great! check them out
Wrote two essays just in case
Practised speaking: figured out all the templates so that i knew what to talk about during those 30 seconds
I prepared for 5 days, so that would be enough if you KNOW english.

My exam should have been in the morning but they recsheduled it for afternoon
Test center was quite nice - great computers but earphones are not soundproof so don't get distracted - concentrate!
Reading was ok, a little bit boring - got couple hard questions so i think that's why 29. my advice after you answer all q's go back to review page! PLEASE DO! one of my q's went unanswered - don't know how that happened so I quickly checked it.
Listening was quite interesting - it maybe weird but i really like listening! just took notes on longer conversations, so that i could concentrate.
Speaking was quite hard because of the time limits of course, be sure to speak after the beep, got a little carried away and didn't manage to finish one of q's in time so maybe that's 27
By the time writing rolled around i was exhausted - wanted already to finish! So just wrote what I could and didn't really worry about it, I think I wrote around 270 words on 1 essay and 370 on second. so if you want to score more there - write more!

So all in all, don't be afraid of toefl it's NOT verbal gmat. and please do it after gmat so your gmat preparation isn't hindered.
GOOD LUCK!!!!