IGN had an interview with Rockstar about the technical problems with the PC version of GTA IV, you can check it out over here.
IGN: What sort of issues are you hearing about, both expected and unexpected?
Kevin Hoare: We're on the forums ourselves monitoring the issues people are having. A lot of these issues obviously we haven't seen in our testing and we're working to reproduce them and find workarounds for those issues. Many of the issues that we've found so far haven't been a direct result of the game itself but rather configurations of driver installations or power management software causing issues, various things of that sort.
IGN: Can you talk about what you're working on right now, like a patch?
Kevin Hoare: We've never stopped working on the game, we're working on it every day. We haven't had the typical break after it's gone gold. We're continually working on improvements, we're working on a patch right now.