[Steve Tinker]

Bala...
What berty is alluding to is the fact that ball bearings in general are limited to several factors determining their suitability - some of which are lubrication, rotational speed / loading and temperature.
With the IMS bearing, the "load" is coming from the tensioning pull of the chain(s) operating the camshafts, so I would think that that kind of lightish loading is well within the design parameters of a deep groove ball bearing.
Rotating speeds @ 50% of engine revs (lets say 4,000 rpm max) @ 100 deg C also shouldn't be a problem as long as the lubrication is constant, clean and of good quality - but that of course could be the achilles' heel of this system.
Ceramic composite bearings have excellent wear characteristics over steel (especially in questionable lubrication areas) but do not have as high a load rating.
Roller bearings (where the balls are replaced with cylindrical shaped rollers instead of spherical balls) have a much higher load rating, but much lower speed tolerance, so would be unsuitable in the IMS application.

As a side note, the grease used for bearing lubrication is really only a lubricant enclosed in a carrier to prevent it being flung off at high rotational speeds - the push fit RS (rubber seals) each side of the bearing also helping retain the lube. Most bearings are "filled" with less that 30% grease (if I remember correctly) during manufacture, any more and there is a real chance the bearing will overheat before it can squeeze out the excess...
I'm sure Navarro, Raby and their bearing engineer have had all these bases well covered in the initial design stage, so you don't have to drive like Miss Daisy.....