All your questions about the copy protection, install limits and other such requirements will almost definitely be answered in the FAQ, so be sure to read it all if you do have concerns.
Initial activation requires internet connection; Online play requires log-in to Games for Windows - LIVE and Rockstar Games Social Club (13+ to register); retail version requires disc in drive to play (unlimited installations for retail discs in most countries); software installations required including Sony DADC SecuROM, Adobe Flash, DirectX, and Microsoft's .NET Framework, Games for Windows - LIVE, and Internet Explorer.
Software with copy protection methods like this are often referred to as being "DRM infested" is often viewed in a very negative light, and you can read about some of the controversy over it on Wikipedia, though you can understand why companies like R* feel the need to use it. As long as you're playing a legal copy you'll have nothing to worry about, except the fact that there is third party software running in the background. At least if you have a boxed retail copy there's no activation/install limits.
We're bracing ourselves for a shitstorm of negative comments regardless. Feel free to fire away in our forums with your opinion on this.