Hello Mihai,
you bring up 2 unrelated questions, i'll address them seperately
1)
Leksah should not be considered an "official haskell ide", but merely one of many community supported editing tools. And frankly one of the less widely used ones at that! Leksah is not used much at all by anyone, though theres probably a handful of folks who do use it.
Many folks use editors like Sublime Tex (2/3), Emacs, Vi(m), textmate, and many more. Its worth noting that the sublime-haskell plugin for sublime text, and analogous packages for many other editors, provide haskell IDE-like powers, or at least a nice subset thereof.
2) There are people working on building better easily portable native gui toolkits, but in many respects, a nice haskelly gui toolkit is still something people are experimetning with how to do well. theres lots of great tools out as of the past year or two, many more in progress on various time scales, and gtk2hs is great for linux (and thats fine).
cheers
-Carter