Maintenance, maintenance, maintenance! As for the 4.9, like Kev said, it's a very good engine. It is aluminum, though, and needs to have the coolant changed with the supplement every 2 years or 24k miles. You don't have to do this, but you risk internal engine damage.
Same deal with the 1995 and previous Northstars. They're aluminum engines and need maintenance just like the Cadillac 4.1/4.5/4.9 engines do. Gorky, do you know the maintenance history of the '94 that blew up with white smoke? Did you buy it new or used? Keeping the oil changed is important, yes, but so is keeping the coolant changed. If you bought it used, you unfortunately have no or little record of the maintenance before you bought it. That's obviously a head gasket problem, and I'd make a wager that the cooling system maintenance hadn't been performed as called for by Cadillac. The head gaskets started to corrode and over time, failed completely.
A great thing happened in 1996 -- DEX-COOL. This coolant has organic corrosion inhibitors which last 5 years or 150k miles. The old green stuff had silicates, which were depleted quickly (and thus the short change intervals). With an iron engine, that's not such a big deal, but with an aluminum engine, it's imperative that the corrosion inhibitors stay in the system! With '96 and later engines, the inhibitors are long life, and it's much less likely to have head gasket failures due to corrosion (there could still be a mechanical problem obviously).