I agree with Aerilius on the fact that using Wine is a good reason for Google to never invest on a linux native version.

However I'll add that, as Sketchup is a close source proprietary program it may encounter difficulties with the core Linux community. First, it will make distribution mainteners unable to create packages for each Linux flavour and so make google in front of a choice of falvours to support. If they develop SU for linux and then make it available only for Ubuntu, that's nice, but that's not the linux spirit and the community will shoot again on Google. If they make a package for hundred of distros it will be a loss of time for every body as they won't be able to focus on developing new functionalities in SU as fast as today (and it's already not so fast as I would like it to be today) . They did the port to linux for GE because it's an ad displaying program. The more people can see the world through Google GE, the more Google earns money. But SU has no ad revenues. The only revenues of SU is the pro version, and most pros are using Win or OSX, and the fact that SU helps the 3DWH to be a huge 3D resource. But a linux version of SU won't probably change the 3DWH size... so Google HAVE to leave SU out of this linux thing. The only way to have a linux version of SU is making it open source so maintainers can make there packages themselves. But I don't think giving SU code to the world is planned by Google. It would be nice, but I think there's more chance that they focus on sending robots on the moon...