We ran into a problem with Google Earth at work and it actually has some use for the people but we had to ban it. The problem is really only relevant if you have a domain network and roaming profiles. The issue was that Google Earth with your typical idiot user gets set to cache a large amount of data. We had users complaining about log in times and I found in many several hundred megs of cached info from Google Earth. I found in one case gigs of data stored and that was the end of its run. I end the end block all google apps ie: desktop, toolbar, picaso, etc. Image viewer/editor apps I generally block as windows has builtin viewer that works for the majority of actually business related images.
Rule of thumb if it looks fun block it.