I have about 25 days on these boots, about 50/50 as far as resort/touring days. I have been skiing the Scarpa T-race for years before this boot came out. In contrast to the T-race I think the Custom is slightly stiffer in the bellows. One big advantage over the current T-race is the Custom has a tour mode and a great one at that. The Custom when in tour mode has a ton of freedom of movement. Compared to similarly big and stiff boots the Custom is lightyears ahead as far as ability to tour. As far fit goes, I was a 28 in Scarpa and I am also a 28 in the BD Custom (I have a 10.5 street shoe). The Custom's heel cup is large and comfortable. There is no need to even snug these boots up for the hike up, I leave all the buckles on the loosest setting for hiking. The boa lacing system in the liner and big heel cup keep my foot right in place. One of my first days touring with this boot we skinned 7,000' and no blisters or even hot spots! So far my only major complaint is with one of the buckles. I buckle my boots TIGHT and sometimes have problems unbuckling the higher of the two lower buckles, especially with gloves on. My solution is to tie on a very small scrap of 3mm cord to the end of each buckle so I can grab that with a gloved hand.

So I have two days on the Customs so far, paired with O1 bindings (RidStiff). I am coming from the black and silver T1's, and I chose these over the Push & new T1's because there is pretty minimal weight difference. I'm 6'1",180 lbs and I ski about 80% in the backcountry, including long tours.
First day was a 30" pow day (pre-heat mold). These boots performed incredibly well once I realized I can't screw around in them- they do demand aggressive action. The skiing was phenomenal but my feet hurt at the end of the day. So, I heat molded the liners and skied the second day in manky wind crust/heavy snow conditions. These boots rocked and my feet were very comfortable after molding. My initial reaction is very positive and I'm looking forward to beating the crap out of these boots like all the rest.
P.S. - I agree with Andy about the one buckle that is a pain in the ass to release. I'll have to rig up something, too.

Since there aren't many reviews here, I'll write one, but please note that my experience with these boots at this point are limited. I'll retract my review when more people start to write in. (Experience so far: two resort days). I'm an ex-alpine ski racer, started to tele ~15yrs ago. This is relevant because I'm used to stiff alpine boots. These boots are buttery compared to alpine race boots, so I was a skeptic when I heard how "stiff" they were. I still concur there; they're not as "extreme" in the stiffness range as people will have you believe. Also, in the store (BD in SLC) I tried the Customs & the Pushes on back and forth a bunch of times and didn't see a ton of flex difference (note: hard to really tell without being locked into a tele binding, and boots were at room temperature).
Existing setup: old T1's (like 3rd gen), G3 bindings, tried multiple pairs of skis.
Skiing: What I did notice right away was that this boot is far more laterally stiff than my old boot. That apparently makes a huge difference, as I was in far more control over the ski edge than I ever have been on teles before. It felt awesome to be able to carve so easily, where it was such a difficult rarity with my old setup.
The bad-news/good-news for me: getting these boots was like mixing single malt with Sunny D, or putting catchup on a prime fillet. They make you quickly realize that you need a much stiffer binding (like the BD 01 or the Hammerhead) to get the benefit out of them. With my G3's, I can lift the heel maybe 2" before I notice the binding providing any resistance. So reader beware, these expensive boots will make you want (or you could say, they require) new bindings and of course some new stiff skis to really reap their benefit.
I'm in line to follow through with the above plan, so when I do (and when I have enough on/off-piste days under my belt), I'll let you know more.

I skied these boots and loved the stiffness and control (almost too much for my 150 pounds). The two middle buckles, however, caught on one another, which is a huge pain. I have a 27.5 mondo.

These boots provide great control. I ski the G3 Reverend with Hammerhead bindings. Last year I had Garmont Syner-Gs; I could control the ski, but I had to do more foot steering than I like and thought it was almost more ski than the boot could handle. The Custom drives the ski really easily. The boot has excellent lateral stiffness, and transfers power to the ski beautifully. I was a little concerned that it would be too stiff for me (I'm 5'10", 155lb), but once on the snow, I found the flex to be smooth and easy. This boot is a huge performance upgrade from the Syner-G. The Boa lacing system is easy to use and provides a snug and comfortable fit. The walk mode does a good job relaxing the cuff of the boot, and the ski mode provides aggressive forward lean. I have not yet toured in them, but they are very comfortable at the resort. If you are an aggressive skier looking for a powerful boot, you will be very happy with the Custom.

I ordered these boots thinking they'd be great for me paired with the rid stiff O2 bindings since I'm a big guy...but I have a wide foot, these boots KILLED me. I wore them one day this season and I was too scared to put them back on, even to walk around the house. I can't write an accurate gear review on these boots but just a warning for guys with wide feet, be aware of the narrow, non-forgiving Customs. Any suggestions for a super wide boot would be much appreciated!

I'm 6'2", 165 lbs. I was looking for a burlier, stiffer boot than my Crispi CXRs, and this one is the ticket. The stiffness of the shell demands and aggressive stance and style (it'll make you a better skier), and the bellows are very stiff, forcing you to weight your dropped ski a little more. However, the stiff bellows provide a nice, progressive flex that tames big powder boards and provides carving stability in a variety of snow conditions. The fit in the heel of the boot is better than any I've skied before, no slippage, and the Boa system on the liner make the boot feel very snug and solid. You might want another pair of shoes to put on at the bar after skiing, but it's a small price to pay for the performance.