I switched to a FREDRIK after the previous HN discussion on standing desks. In general, I am quite happy with it, but some notes from my experience:

You cannot adjust the height of the shelves without taking most of the desk apart. The increments are fairly course, so it may be difficult to get the height right -- I had to dig up the riser which came with my Microsoft Natural keyboard.

I use it with an IKEA bar stool and often switch between sitting and standing a few times during the day.

picture: http://www.flickr.com/photos/kuno/5053375629/

I will second this. Make sure you're looking at the $150 Fredrik "Computer work station", not the $100 Fredrik "Desk". The Fredrik has extremely solid steel support. I've used it for over a year and a half, most of that time as a standing desk, and have disassembled and reassembled it at least a half-dozen times (for height-adjustment of the desk or shelves or for moving). It holds the weight of a 24" iMac, a second display, a stereo receiver, and two shelf-lengths of books with no bending or bowing whatsoever. I even have a habit of leaning on it when I'm not typing, and it's held up to it perfectly.

That looks very interesting (particularly as it's a desk which is widely available across countries) but 98cm max-height seems a little short for a 6' 2" guy like me? I'm assuming that you elbows should still be at right angles (i.e., that the same rules apply whether sitting or standing)