Do you know if this will have any implications for applications built on it (will they be forced to use GPL)?
This is how Trolltech used to charge money for commercial use of Qt. Qt was dual-licensed under the GPL and a commercial license, so GPL'ed software could freely use the library, but non-GPL software would have to pay for the commercial license.
I should start writing * GPL as I do with * BSD
As for linking proprietary code do GPL'ed libraries, the license is not explicit. However, according to Larry Rosen (http://en.wikipedia.org/wiki/GNU_General_Public_License#Poin...) linking, even statically, does not make a derived work (that would be subject to being GPL'ed by accident). Also, the GPLv3 has some different wording. I understand the GPLv3 makes it less likely a program linked to a GPL'ed library will be considered derivative.
From the GNUStep site (http://www.gnustep.org/information/aboutGNUstep.html):
"The GNUstep libraries are covered under the GNU Lesser (Library) Public License. This generally means you can use these libraries in any program (even non-free programs) without affecting the license of your program or any other libraries GNUstep is linked with. If you distribute the GNUstep libraries along with your program, you must make the improvements you have made to the GNUstep libraries freely available."