I used CrystalDiskMark to compare two machines and -- as expected -- the speed difference is signifcant!
Here is a benchmark from my desktop machine with an HDD:
(larger numbers are better)
And here is a benchmark from my laptop with SSD:
NOTE -- an ideal benchmark would be in the same machine before/after an SSD upgrade so this isn't a perfect comparison, but I think overall the results are representative.
Before the advent of SSD's, I always told people that the simplest cure for a slow PC (that is -- for the average user home/business user who is going to surf the web and check email and balance their checkbook in Excel) was to double their RAM.
Now that SSD's are around, in most cases I would probably make an HDD->SDD upgrade my #1 recommendation, and RAM upgrade would be at #2.