For US allo schools 3.0 is pretty much the minimum realistically required to get in. There are exceptions of course, but they're few and far between. DO schools replace grades upon retake, so it's easier to boost your gpa there, plus the standards are lower. So, basically, if you have a 2.3 it will probably be prohibitive to take enough courses to get yourself over 3.0. There are also differences in requirements for sponsorship depending on your gpa. There are plenty of people in the 3.0 range coming in, however, that get into good schools (I'm guessing top schools are somewhat rare in that case, but I'm sure you can figure that out...) People go to HCP for various reasons - some to raise their GPA, some to take the pre-reqs for the first time, so you see a wide range of incoming GPAs
If you get sponsored your chances of getting in somewhere are very high. I forget the exact number, but I believe it's around 90% success rate. They don't sponsor people they don't think can get in.