Firstly: treat every hard drive that you use as though it might fail tomorrow, and you might then consider a safe backup protocol that includes taking copies of valuable data offsite, and regular backups.
There are two main issues with Lacie drives. Firstly they run very hot, so leaving them powered up for extended periods of time tends to overheat the drive mechanisms inside thus reducing life expectancy. On the other hand the connectors are dreadful, so multiple unplugging and replugging cycles of the power supply and Firewire connectors results in premature failure.
Personally I look for an enclosure that has adequate cooling, and an onboard power supply with an IEC mains connector. Most of the external supplies use frail cable for the DC supply and under-rated connectors.
I miss the old Sarotech cases with the slide apart design, they were great although inclined to bridge board failures.
I don't think there is any one design that is particularly great, like most things these days they are designed with increasingly shorter "Mean Time To Failure" engineered into the build.
Bottom line: multiple copies on multiple mechanisms, stored in multiple locations!!!!
