Pre LCi 330d's have the 'bulletproof' engine. The M57 with the revised swirl flaps... I don't think there has been a reported swirl flap failure in a E90. That's pretty much the only thing that killed the engines in E46 330ds.
This said, mine was a very early N57 engine so possibly they 'revised' the design of the guides. When I check the part numbers fitted on the online catalogues I don't remember the being any superceeded parts.
It is still a great car and great engine but definately not a characteristic that should be present in such an engine. I would rather have a front mounted serviceable Cambelt that you expect to renew at specified intervals. Timing chains shouldn't require any servicing, certainly not within 150K...maybe at higher miles 200-300K which will only account for a small percentage of E90s in the future.
E90 330d - N57
Prof Nav - 6FL - Visability Pack - Alpine Hi-Fi Upgrade - L7 Subwoofers - L7 rear mids + tweeters - 6FL