And yes, drive speed is very important. LR working speed greatly increases going from a slow drive like an internal iMac (5400 rpm) to a desktop 7200, to a raid0 array. Anyone that says otherwise never tried it. It's seen in importing, exporting, rendering and more. Those are frequently used parts of it and it's well worth it to maximize all parts of your performance.
I have to disagree with some of those statements. There's nothing wrong with maximizing all the parts of your systems performance, but don't expect dramatic improvements in importing, exporting or rendering by getting a faster drive. None of those processes bump up against the capabilities of a mainstream internal 7200rpm drive.
Importing? You are capped at the speed of your CF card reader. Even a 1000x card and a USB 3.0 reader won't be faster than 7200rpm SATA drive.
Exporting? You are generally capped at CPU performance. The only time you might run up against drive speed limits is if you are exporting a large number of high resolution 16 bit uncompressed TIFF files. Exporting jpeg files will probably happen at around only 5-10 megabytes per second, where as exporting uncompressed TIF's might reach 80-90mb/s depending on how fast your computer (CPU) is. Even the latter is within the capabilities of a 7200rpm drive.
Rendering previews? Again, this is limited to CPU power. A fast computer might render 1:1 previews at a rate of 2-3 seconds/preview for a larger DSLR file. This equates to a data transfer rate of only around 10 mb/sec off the hard drive.
And as far as having tested it... I have.
Outputting 16 bit uncompressed TIFFs (1Ds III files) to an SSD vs to a mostly full 1TB 7200rpm drive? Pretty much no difference, both wrote at around 80mb/s, limited by the CPU's ability to export the images. Same results with exporting jpegs, except data rates were only around 7mb/sec.
Importing and rendering 1:1 previews? Exactly the same amount of time, whether the images sat on an SSD capable of 500mb/sec or whether they sat on a mostly full 7200rpm drive.
The only real area where you see performance improvement from a drive change is when the Lightroom catalog sits on a faster drive, especially one with lower seek times. And this doesn't help any of the importing/rendering/exporting processes. It only helps images display faster in Loupe/grid view, making navigation seem snappier.