The first thought that comes to mind for me is anti-trust. I say this falls under the same category/umbrella as Windows and Internet Explorer. Google's penetration of just over 70% is slightly lower than Microsoft's was, I believe, but I would imagine that type of dominance could easily warrant an investigation in the least. Google is
already under investigation
related to digitizing books, so this wouldn't be out of the question.
Now, how would it affect the ILS? Well, Ryan is right that in the short term they aren't capitalizing on this, but how long is that realistically supposed to last? Google already knows the top search phrases for real estate search, so they will artificially dominate every one of those. Once that happens, they immediately give themselves incredible market share, almost by magic. Those ILS's that depend on dominating the high traffic search terms will be impacted the quickest, in my opinion. Those that have focused on long-tail searches may be a bit better situated, depending on how far Google chooses to implement their results.
In the end, Google is violating their own concept of putting the most relevant content at the top, so will that result in any user backlash? Only time will tell...