Well...
I use(d) my PocketDISH everyday for at least 2 hours. My mainstay was Sirius Radio and SD shows I recorded specifically for my daily use. I also have about 500 DVDs converted to Divix and typically stored about 15 on my PD for emergencies. I also search for premiums movies to record both for HD at home and for SD on the go.
I know of no other PMP that allows one to get so much free content (not really free since I'm paying my bill), everything else like Iphone needs to have content purchased for $0.99 to $2.99 each or your converted DVDs or CDs. I know I enjoy recording Saterday night Siruis Beat Remixes and them having new current remixed music available without having to buy something on Itunes.
I have as much HD as anyone else, but I also have the SD versions of each channel. I pretty much know what TV I'm going to watch at the gym, so if there is an HD show I watch at home and might also watch at the gym, I'll record both versions.
IMHO, it's a great product that for $100 per year (my $300 PD lasted 3 years) added to my $1500 per year sat bill, it is very well worth it.
I would guess that someone with Turbo HD only would not have any use for these devices. I would also guess that someone who does not have a standard use of these devices might also not know how to program their DVR to use it. Recording all shows in HD won't work for someone who simply might wish to plug the PD in and load for on the run. I have to plan my SD recording for my PD ahead of time, when that is done (takes a few extra minutes once a week), I can plug and load while getting dressed in the morning without issue.
A device that will load HD and SD will be a great addition. With the 320GB of the Archos 7, there is at least room for HD content, but I would imagine it would take one hour for a two hour HD program to get transfered anyway. That is not really practical.
I had my PD was before there was so much HD, I simpley adjusted my recording behaviour as HD became more and more abundant so that I could enjoy both HD at home and my PD on the go.