I think this sums it all up. This issue riles up the people who don't trust Clinton, and were never going to vote for her anyway. The rest of us are not bothered.
There is a group of people in the country that will not vote for a Democrat and there is a group of people in the country that will only vote for a Democrat. I agree that this incident did not effect that reality. In addition there is a small group of people that are not going to vote for Clinton because they don't like her for various reasons even if they are Democrats. This incident might have increased the size of that group a bit.
There is also the reality that Clinton nomination is not a slam dunk and this incident has undoubtedly energized some of the potential opposition candidates a bit and as such this incident is politically significant.
The next presidential election will probably be decided by moderates in swing states that might vote Democrat or Republican depending on what their ideas are about the specific candidates and this incident has hurt Clinton with that group. FWIW, this looks like one of the first real scandals of the Obama administration to me (most of them were manufactured completely or massively exaggerated by partisan spinners). But I agree it isn't a major scandal, it is just a real one and that will hurt Clinton with the moderates.
Clinton looks worse on this incident than some of the partisans in this thread would like to admit. She looks:
1. Elitist - The rules only apply to other people
2. Evasive - There must be something she intended to hide with this scheme.
3. Naive about digital security - How does she know that this little private server of hers was adequately secured?
4. Naive about the reason for the rules - Her defense that she wants all the emails made public excluding the ones she decides not to make public makes her sound stupid
5. Out of it - People expect to use their company email for work and their private email for private communications for a raft of reasons. She seems to have been unaware of that if you believe her silly explanations.
Still, I'm a registered Republican that will probably vote for her if she gets the nomination instead of some war happy, science denying, government shutting down Republican.
ETA: Has anybody been identified as the Eric Hoteham yet?