If memory serves me properly, HP also has longer warantees; somewhere along the line I also gathered the impression that HP is more likely to make software updates readily available without support contracts or registration, at least for their switches.
My experience with HP switches is fairly limited; I have had a couple of occasions in which to examine the offered facilities on some models in order to make recommendations. In my limited exposure, what I found was that:
a) HP switches are generally less flexible; for example, for QoS, you only had the option of doing this-kind first and then that-kind, and there was no possibility of doing just that-kind or of doing this-kind within a that-kind stream. They assumed you would always want to do QoS one specific way, and if that didn't match your needs, you had to go without (or go to a different vendor.)
b) HP switches seem to be released with significant inherent functionality that is not enabled in the first few software releases -- e.g., when they started releasing their Layer 3 Switching models, they marketed them as supporting Layer 3, but when you read the manuals it turned out that you had to wait somewhere close to a year to actually use the feature (thinking back, this might have been "using a routing protocol" on their switches: static routes were, if I recall, possible from the outset.) But policy-based routing.. no go, even on their enhanced software (at least when I was looking.)
In the scenarios I was examining, I couldn't recommend the HP switches. They looked decently fast (at least on paper) and priced well, but the lack of flexibility and non-present functionality made them suitable only for "buy now, replace later" scenarios. That is, there is a school of thought that says that you are better off buying only on the basis of what you need *now*, because by the time that upgrade project is funded and the requirements documents produced and so on, there will likely be another model on the market that will do the future requirements cheaper and faster. Often, though, when you are buying Cisco, you are doing the opposite, buying into "we're headed towards X, so get something that will readily accomedate X when it arrives". The Cisco equipment is likely to survive redeployments and "hand-me-downs", used and reused and abused for purposes not imagined when it was bought; I don't get the same impression for HP switches.
Depends on what you want to do. If you want a basic managed switch, they are simular. If use some of the much larger feature set of Cisco, you'll be missing quite alot on the HP. If you don't use so many advanced cisco features, then probably not a big deal.
But, if all you are looking to do is basic switch functions, the HP (or even the Dell line) works pretty well for the price point.
I got a call from an HP guy the other day, inquiring if we still use their Kit. I told him our network is 99% Cisco these days, and that we only have about 4 HP switches left, and that we were changing them to Cisco.
He asked why, so I said to him, "Cisco are the best in the world, can you tell me other wise?"
He didn't say a word!
It doesn't really answer your question, but it says a little something.