I have the 68K which isn't all that different from the 70K. I tried on the Tacks line as well and had the same experience as chippa13. The new Ribcor line gave me more volume thru the instep/arch area. I generally fit into a deep boot like the Nexus or Graf 709 but have a narrow heel (wide v-shaped forefoot but with thicker ankles and a lot of volume in the instep/arch area - the Old Easton S17 were the best fitting skates for me).
I have to agree with everyone that, for me, it's been the best fitting skate in years. Despite what the websites say, I'd call the new Ribcor line a medium, mid to mid-low volume forefoot, mid to mid high instep volume, and mid ankle volume. It reminds me of the Easton S17 fit but lower cut or the older CCM Tacks fit from the 90's but wider in the forefoot and stiffer.
As FlyingChicaga and Rockingsquat said, it gives great heel lock and is really comfortable once broken in but it does expand a lot when its baked and it does keep breaking in and give you more volume over time making it difficult to size the skate properly.
I'm a 6.5 across the board for skate size (excluding some of the odd sized skates like the first gen Tacks and Jetspeed) and these 68K's have now broken to a point where I think I could have gone down to a 6 if I really wanted (Toe are just barely not touching the cap standing up now). Just a word of warning, I like my skates really short to where my toes are touching the cap so I just added some Powerfoot to keep that feeling.
Overall, I really enjoy the cut of the boot, height, and the flexibility of the boot. Don't get me wrong, the boot is plenty stiff enough but it has just enough flex built in to where it doesn't feel like ski boots on your feet when tied to the top (For reference I weigh about 230 lbs.). Once I get more time in them, I'll write a full review but so far so good. Also, it looks like CCM might be using slightly thicker eyelets than their previous incarnations to prevent the eyelet issues it had before but this is just from looking at it with the naked eye.