Good news for all developers! QT will be available under the LGPL starting with version 4.5. The GNU Lesser General Public License (LGPL) is a free software license published by the Free Software Foundation. The LGPL places copyleft restrictions on the program itself but does not apply these restrictions to other software that merely links with the program. There are, however, certain other restrictions on this software. The LGPL is primarily used for software libraries, although it is also used by some stand-alone applications, most notably Mozilla and OpenOffice.org.
This option could increase Qt usage and adoption. You may see more cross platform commercial application on the Linux desktop. This is huge news for cross-platform developers.