I for one have never tried any kind of IDE drive in my SE/30, more less SSD's. But I will admit that I want to try a flash drive in my machine at some point. Manabu Sakai of ARTMIX has long sold a flash card adapter setup for the SE/30, but it's not cheap and he refuses to give real world comparison feedback on how fast it is versus a normal 7200rpm spinning platter hard disk.
But you know, what would really be THE ULTIMATE solution is a custom made PDS card with 4GB or so of memory. Bypass the SCSI interface altogether and have your drive connect direct to the processor. It would be like having a RAM disk that never loses its contents. Not sure how compatible that would be, but I would LOVE to see something like that appear!