My new SB13-Plus arrived last Friday and I've been using it most of the weekend. It cost me a small fortune to get here (New Zealand) and I ended up having to go and pick it up from the local CEVA depot (delivery was extra, even though I paid US$280 for door-to-door delivery...). They actually loaded it into the back of my SUV (that I had to borrow) with a forklift, on its little wooden pallet. I wasn't expecting it to be quite so challenging given that it's not actually that big.
This sub is built incredibly well. The bass is produces is equally impressive. I haven't had too much experience with subwoofers (I have had a Velodyne CT120 for over 12 years; before that an Energy then a Polk sub) but the improvement was dramatic. It's being used with a new set of front speakers (KEF Q900 and Q600c, replacing B&Ws), so it's hard to tell what is responsible for what (everything changed over in one go). The bass is much deeper than before, but what I like most is just how tight and musical it is. It's the sonic equivalent of a velvet-covered club. I think I'm a sealed sub convert, and I'm even thinking about getting another SB13-Plus (before the Ultra comes out, so I can have two cosmetically matching boxes). I suspect this sub will be joining the few permanent members of my home theatre.
My only suggestion would be for SVS to get someone to proof their user manual. It could really use some work.