Just my personal take: Compatibility with Apache 2 license is huge. I would guess that most developers of software under GPL and Apache licenses would like to enable people and organizations to build new open source software with both GPL and Apache licensed components.
Another reason why GPL v3 is important: there are too many open source licenses right now. If GPL v3 is successful, then I hope that an even larger percentage of open source projects use the GPL. While some corporations do everything that they can to lock in business by spreading FUD about open source and using non-standard file formats, it is in the general public interest to have a strong open source infrastructure and standard document formats. Standards in open source licenses are also important which is why I would encourage standardization on GPL (and LGPL), Apache, and BSD - whatever developers feel is right for their projects and their personal philosophy on open source. I believe that there is also no problem mixing BSD and GPL modules in the same system as long as individual licenses are included with any distribution.
While my projects are currently LGPL I prefer the GPL. LGPL has one huge advantage: LGPL licensed code can always be used under the GPL license. I LGPL my projects to let more people and organizations use my work but I am considering changing to GPL v3 in the future.