The HP ProLiant line has proven to be a very durable and reliable product. This is the greatest thing that I love about HP servers. They just work and keep on working. We have HP ProLiant servers which are almost 10 years old and is still working until today.We bought HP ProLiant servers as they offered us the best value for money in our part of the country. HP also has great support countrywide, and we didn't have any problem that the local support could not handle. This for me is the number reason why selected HP ProLiant for our servers in our part of the country. We felt more at ease with HP ProLiant rather than with IBM System X, as HP has better support.
Room for Improvement:
The only con I can think off with using HP ProLiant is the limited parts of the old servers. This is understandable though, as it is also not feasible for vendors to stock parts which might never be sold.There is also this thing about server management. Other vendors like Cisco has really taken leaps and bounds in overhauling server manageability and make it work. HP has had new products as of late, but I think they must have innovated sooner as they are now behind the competition in this regard.
I would definitely recommend HP ProLiant servers. They are very reliable and very easy to configure. Just make sure that you stock-up on parts which you think might not be available any more in the foreseeable future. From experience, stock on the hard disks especially if you are still using the older technology, and buy redundant power supplies as these are the ones that normally fail after years of continuous operations.