I'm thinking of building a piece of software on top of another piece of software which is licensed under the GPL. I am planning on licensing and selling the software.
Could anyone who is familiar with the details of the license see any problems or pitfalls of having a dependency on a piece of software licensed under the GPL?
If you mean GPL, then you have to release the full source code of your product and tools needed to build it. If it is GPL3 and you also sell hardware you have to make sure customers can replace the software on it.
If it is LGPL then you may link to it without the impact above, but not statically!
Subjective: Personnally I think GPL is far too restrictive, I would look for alternative projects under MPL or BSD-like licensing models you could build your software upon.