I was hunting down the programs that write constantly to my SSD drive and I found that my Opera writes constantly, with an average rate of 130KB/s (or every two seconds), to this folder:
C:\Users<user>\AppData\Roaming\Opera Software\Opera Stable\Jump List Icons
It turned out that the refresh of the pinned sites from the "Speed Dial" causes those writes.
A simple calculation shows that for a day the total writes would be: 130KB x 60s x 60min x 12h = 5,616,000KB ≈ 5.3GB !
And for a month this gives: 30days x 5.3GB = 159GB !!!

I don't know why Opera has decided to update the icons of the pinned sites every 1s/2s, but I would recommend to anyone with a SSD drive that uses Opera to disable the "Speed Dial" component.