The company behind Qt has been getting very passive-aggressive in the last 1..2 years about using the LGPL version for commercial projects. They didn't shut it down (yet?) but they're definitely not happy about it. Personally I wouldn't consider Qt for future projects because the writing is on the wall.
Luckily the LGPL license can never be revoked on previously released versions. So it's possible to use Qt 5 and never have to worry (as long as you follow the requirements of the license in terms of dynamically linking the libraries).
That’s true for 6 as well. I believe there are clauses in Qt’s ownership documents that prevent it from ever becoming closed source without automatically invalidating previous licenses and becoming GPL-only, or something to that effect. The poison-pill was designed when Trolltech first sold away Qt, if i remember correctly.
