Mid-air movement controlling
I still making my map #3 and since there is a scene when I neeed the player to gain height so later he can jump down 2x times to reach the floorlevel of the starting corridor to get a cube, I made a small vertical room. But instead of making it just a simple portal-up scene, I decided that I move an element from my map #4 here (that a bit harder). To solve it the player must control himself in the air while falling.
I just want to know if its too hard for a not-hard map or is it ok?
First just try the included map-part:
http://heroes.hardwired.hu/-/portal/por_damagepy_03_tmp.zip
Is it easily solveable? I mean the air-controlling, not the puzzle, since its obvious what to do.
An example video:
http://heroes.hardwired.hu/-/portal/midair_forward+strafe.avi (do not view it if u not tried the map yet)
Please rate its difficulty from 1 to 10 (10 hard). First I wanted just a small trick when the spot was under the upper portal, and only a small 32 pixel midair movement was needed, and I actually didnt know I can move this much back using this technique. I have more extreme ideas for map #5 but if a player only tries to use forward movement or slowly moves out from the upper portal and only starts moving when he starts to fall, he never completes this part.
Also there is a "bug", sometimes if I run to the portal located downside, and I jump in the right time, then when I excit the uppar portal I receive a weird thrust and I manage to simply land on the upper level. Only happened once, but still, its weird, when the portal pushes me out that hard, and I can't really reproduce it.
This is something of a coincidence, for I too have an air-control fling puzzle of sorts in an upcoming map.
That said, I find your puzzle perfectly acceptable and solvable from a difficulty stand point; I can't imagine many players becoming stuck or frustrated.
At most it will take a few tries. Easy enough to execute and the intention is clear.
I'll have to try it when I get home. . . it sounds like its not too difficult, judging from the responses. 
One thing; if it IS going to take a fair number of attempts to get right, then the best thing to do is to make sure its something you can fail at and easily portal-back-to-retry, instead of always dying an ugly death and have to restart. Fixing that goes a long way towards making things like this bearable. . . .
I didn't see the video when I did it, but when I saw it actually I solved the puzzle in another way. I'm going to try to make a demo and give out a video link.
The way I done it is because one of my future puzzle projects involves that kind of special jump.
http://www.hurricaaanes.info/ai/portal/023_edited.avi
EDIT: I found an even easier solution. Please wait.
Author of Minecraft mods (MAtmos, Minaptics, NoteSlider) and Garry's Mod addons (Gunstrumental, SharpeYe, GarryWare, DepthHUD).
I was eventually able to do it the intended way, one of HUricaanes ways (the last one) and also a way where I dont even turn right when I leave (I faced forward while sidestepping and going backwards). I think your original way is the easiest though.
Since there are so many ways to solve it, and since there is not much cost or setup-time for a person to try different methods (you can try this 20 times in a minute or two), I wouldnt rate it too difficult. Perhaps a bit on the irritating side, but then some puzzles are like that.
I also did this 3-4 times; twice in a row once. You get that higher pitched sound than normal when exitting the portal and you get pushed right across. I ALMOST felt like I had a handle on what was going on, but I never could do it more than occasionally. . .