Read this story indicating that the HP tablet is struggling for sales in the US, indicating that further discounts are possible (Recently it was reduced by $100).
In a nutshell sell through at stores like Bestbuy is quite poor (10% or less of total stock that Bestbuy has).
http://allthingsd.com/20110816/ouchpad-best-buy-sitting-on-a…
I think it's similar to Nintendo 3DS. You can discount it further, but it still won't pick up the momentum if there's no apps/games for it. Same with RIM PlayBook IMO.