Wouldn't touch it...
... with a ten-foot eSATA cable.
Like some other folks here, I'm sticking with spindles until flash attains both cost **and** write/rewrite cycle parity with mechanical drives.
However, as a rule of thumb, I never use a desktop drive with more than 2/3 -- or a laptop drive with more than 1/2 -- the storage capacity of the form-factor's highest-capacity, bleeding-edge spinner.
For me, this means that I currently provision desktops with 2.0TB to 2.5TB drives, and order laptops with 500GB to 750GB units (depending on make/model/use pattern).
Bleeding-edge magnetic storage always seems to pack the bits that much "too close" together to provide the reliability I require, so I like to stay a generation (or two) behind.
Flash and spintronics-based storage technologies hold a lot of promise, and are undoubtedly the future, but are not (in my opinion) quite ready for "prime time" use as primary storage. Once consumer-grade flash can endure 500K writes per cell, at densities to allow a 500GB unit to fit in a 2.5-inch form-factor, and cost less than US$250, I'll switch.
But until then, I'm hangin' with coated flywheels...