This has been a very hot topic on many threads. Hobie did revise their manufacturing and reduced the diameter of the holes in the 3/4 x 1 x 6 inch aluminum spacer, I believe the reports of masts slipping on newer hulls has greatly reduced (mostly because everyone is checking their bolts often). I don't have a front cross bar slipping problem on my 2012 TI hull, but I did have that problem on my 2010 TI hull (it was pretty bad), my 2011 TI hull would slip until Hobie sent me a new aluminum spacer block, after installing I no longer had xbar slipping problems, but had to make sure all the bolts stayed tight (checked often). I have also noticed on my 2012 TI (from the factory) that Hobie has the Harken blocks for sail control and furling back in their original (2010) position, one on each side of the outermost hull clamp, this limits the possible side to side movement of the forward cross bar to less than 1/4 inch. In addition my 2012 TI has the improved cross bar with weld in the front and back of bearing plate. Bottom line is, In my opinion is Hobie has progressively improved on the mast holder design based on feed back from users and 2012 and onward owners should have much less problems than previous designs. However it is still very important to check all bolts often ( I inspect everything before each outing)
As a side note, and related subject I made what I think was a pretty big discovery on page 3 of the thread Mast Support Fail ( viewtopic.php?f=71&t=44081&start=60
This is related to the mast strength, and lack of support for rearward and forward force on the mast holder. Basically I suspect many of the studs at the bottom of the mast cup that have broken, have broken due to forward or rearward force, rather than side force as I believe everyone was suspecting. Basically what I am saying is if all the bolts on the frame and v-brace system are tight, it is still very easy to snap the stud in the bottom of the mast cup, by either sailing in a strong gusty downwind condition, or pulling the sail too tight when sailing up wind. You can likely snap that stud by simply pulling sharply on the sail control line (pulling the sail very tight) with the boat sitting in your front yard, "because of the great leverage".
Since re-enforcing inside my hull with both the aluminum piece epoxied into the hull, and the strap wrapped around the forward drive well (mentionioned later in the thread) I have had no difficulty with my masts. As everyone knows I have huge sails on my TI's (designed to suit local " low wind" conditions), and have used all these sails extensively in sometimes not so desirable conditions. I no longer have any fear of damaging the hull.
Hope this helps