It's highly competitive in terms of cost and performance. There were other players, but one after another, they disappeared. If you ask your customers what's most important to them, it's always cost efficiency. They always complain about paying way too much. With HP, they're getting the best product for the money.
Room for Improvement
The most improvements that could be made would not be in the hardware commodity itself, but in the firmware. There's synergy between hardware and software, so you can't view hardware in an isolated way. So the improvements I'd suggest would be in the software that runs the servers.
Use of Solution
I've been using it for 15 years or so.
We've had stability issues, but they weren't anything that other vendors don't have. In particular, we had problems with the DL585 generation 7. It has what we call a "Monday product", which is not hard to fix, but we've had much more trouble than others. These problems seem to be recurring for us.
For our scenarios, it's scalable.
Customer Service and Technical Support
We don't get direct technical support from HP, but rather from our partners.
Overall, we have a good partnership with HP and we are heavily invested in them.