HP1000's refer to the set of Grado's highest-end headphones from their previous line. They are out of production completely, and are very sought after on the secondary market. Most who have tried them find them far better than Grado's current top-of-the-line, the RS-1, many put the HP1000's as one of the top dynamic headphones of all time.
1) They are on par with the RS-1 in the current lineup (although I believe they were considerably more expensive new).
2) I know of no 'professional' reviews of the HP1000 series, but if you search these boards (or browse the full-featured headphone reviews) you will find quite a few reviews of them, most by individuals with more headphone experience than any 'professional' reviewer.
3) No shots necessary. BTW - If my understanding is correct, the HP1000 referes to the series of three headphones: HP-1, HP-2, HP-3. HP-1 being the best of the three (although all are said to be very, very similar).
HP1000's are in serious demand, in this market finding a pair in good condition for $1000 would be considered a bargain by some, just because of their rarity.
Basically, this would be way overkill for 'your mp3' - if you could even find a pair. I wouldn't recommend this caliber of headphone to anyone without equipment of equal status (source, amp).
-dd3mon