If the 3 nodes that hold a specific fragment you want to download go offline at the same time, you won't be able to access that fragment until one of them come back online. It's a scenario that's unlikely to happen, but Murphy's Law shouldn't be ignored either.

I personally don't think 3x redundancy will be enough with the current reward system. The retrieval speed of files and file availability will become an issue at times. Essentially, downloading your files from 3 nodes, is similar to you downloading a file via BitTorrent with 3 seeds. More often than not, if those 3 seeds are just at random locations throughout the world, chances are your speed will suck.

Now, if Metadisk/Storj early on implements a scheme to reward not only available storage space, but also stability and speed, then I can see 3x redundancy working wonderfully. A project like Storj will depend an awful lot on the stability of its network, and since it's decentralized, also on how many people are using it AND using it while having a good experience doing so.

Incentivizing stability and speed is key. Otherwise you risk ending up with humongous amounts of unreliable and slow storage space.