for me, it wasn't a small change in performance - it was significant and instantly noticeable. my ocz vertex 2e cost about £90 - what other upgrade can you get for that money? some more ram? i've got 4 gigs - that's enough for me.
so what will an ssd do for you? faster boots, and a snappy responsive operating system with faster app loading. even big apps like photoshop open in two or three seconds. it isn't just 'five minutes over eight hours' - it's every single time your computer reads or writes to the drive. random access time is phenomenally low.
i don't think anyone with an ssd will ever go back to a spinner.
but feel free to not believe me, and put it all down to hype if you prefer.