I just replaced my old VIP622 with a VIP722k I bought off on the classifieds right here on Satguys. Got a fantastic deal, and it works much better than the old 622. I also now can use a Slingbox adapter if I so choose to do so, and you can't with the 622. I would suggest you go to a 722k also if you purchase. However, it is true that Dish will replace even a purchased receiver with a like model for a small fee. You will still own the replacement receiver. In my case, I wanted an upgraded model, and bought for a price not that much higher than what Dish wanted to replace the 622 with an upgrade model. It is still possible to buy a replacement harddrive, but you can expect to pay at least $95 for the drive alone, if you can find one. You can NOT just use any drive, it has to be one special made for these receivers. Dish will swap the whole receiver for less.
Check with a DIRT tech right on here for particulars if you decide to just swap straight across for another VIP622.