The logo is pretty but I would not use it for one simple reason:
This logo promotes a license, not a system.
OGL does NOT equal 3.5 system. OGL is a way of releasing game material, and has been used to release the d20 system via the SRD/MSRD, but also the Action! system and the Fudge system and the Fate system. All those are OGL games, not to mention M&M, True20, a crapload of stuff released by Mongoose, etc. This logo does not help me tell my customer that my product is 3.5 (yes, I know it says 3.5 System, but it's the smaller font, and at a reduced size, it clearly becomes the secondary message conveyed).
The reason this is such a sticking point is that the OGL does not care what system it promulgates, but for far too long people have used the terms "OGL" and "d20 System Compatible" interchangeably when they are not. This in turn has created the very issue that is now being debated where the 4e GSL is trying to curtail 3.0/3.5 support and erroneously used OGL as a substitute term, which in turn had the effect of creating a much more draconian reading of the purpose of the license.
Make a logo that indicates 3.5 rules compatibility first and foremost and then there might be grounds for consideration.
Again, OGL does NOT equal 3.0/3.5/d20 System compatible.