Slyster,
I may be able to answer you as I'd been a Dish customer since 1997 and recently made the switch to DirecTV.
1. On my R15 DVR (DirecTV Plus DVR), there is a 30 second skip forward button. You can press it multiple times to also do a 60 second, 120 second, etc skip. It's like a fast forward though in that it rapidly scrolls through the 30 second skip, guess that's how they answer the NAB's concern over missed commercials.
2. It's the R15 for SD, available as the R15-500 and the R15-300. The only difference as I understand it is the manufacturer, the R15-300 is made by Phillips.
There's a new HR20 for HD DVR, but that's being released arround middle of september. If you get HD DVR right now, you'll likely get the older HR10. HR20 is MPEG4 capable, the HR10 is not.
3. As to the difference in quality? I think I perceive the D as slightly sharper and crisper. This may be attributed to the "It's new syndrome" and effecting my perception.
Of course, promotions change, but if you check out the current offers they are very attractive. Looks like the Dish to DirecTV promotion is simply an extension of the current promotion to Dish customers. The current promotion winds to a close on August 31st. Myself, I've got a free portable DVD player on the way and 15 $10 credits for my monthly bill (the $150.00 rebate offer), I also got my SD DVR for free with programming commitment. As a former current Dish customer they wanted to charge me $99.00 to replace my failed DVR, pay a lease fee in addition to the DVR fee. That added up to 10.00 more a month to have a DVR for my Top 120 package than it did under my previous DVR setup (had one of the Dishplayer 7100's).