I don't often get to turn my amp up, so I needed something that would let me practice guitar quietly at home, and these phones do the job. I had been using a Logitech headset (the kind you use for Skype), and it was okay, but everything sounded squashed and tinny. For $20, I decided to give these a try before spending $100+ on a pair of pro mixing phones.
Upon firing these up for the first time, everything was much more open with a lot more detail, good bass, and the highs weren't shrill or piercing. After using them for a couple of days I think the highs may be a little too subdued on these, but otherwise I don't have any gripes. They are incredibly comfortable, so much so that I forget I'm wearing them after a while.
I run a POD HD500 into my iMac and use the HPS3000s to monitor (plugged into the headphone jack on my computer, not the POD). The connector is 3.5 mm, but it comes with a 0.25-inch adapter for plugging into a mixing desk or pro sound card. I don't recommend plugging these or any other low-impedance phones into a POD HD500 — the headphone amp on those is horrible (they recommend 150-ohm phones or higher, but good luck finding those for less than $200).
The HPS3000s are great for what I do, and I imagine they'd work for any hobbyist who doesn't have the scratch for pro-level gear. I had a pair of Audio Technica phones a couple of years ago ($150), and i sent them back because they sounded awful with my POD. These sound great, and I'm incredibly happy with my purchase.