I think the "future", at least for the masses, is probably a hybrid of SSD + HDD. I am thinking maybe a small/cheap (16GB?) mSATA SSD and a large HDD. Use the small SSD only as a cache - your OS, apps, and data are all on the HDD. I've seen some really impressive benchmarks from systems configured like this. If the SSD fails, then nothing is lost except that your system doesn't run with the benefit of the cache.
What I know for sure is that 128GB (or larger) SSDs are too expensive (and/or not enough space), and having SSD + HDD as separate drives (C and D) are too complicated - at least for most people.
It could be more effective to increase the RAM in the system and use that as automatic cache rather than use an SSD. Main memory is rapidly falling in price and is much faster than any SSD would be for that use (non-persistent storage). The W520 will support up to 32GB for quad core CPU configurations and there are several DRAM suppliers whose memory kits are less than $150 for 16GB.