Big time improvement. My vision was -6.75 (can't see the big E on the eye chart unless I was 2 feet in front of it) and is 20/15 now.
I waited until I knew about a dozen or so people who had it and they all were thrilled they did it, as am I (wish I'd done it sooner than I had).
I opted for PRK, not LASIK (why have scarred corneas when you can grow new ones?).
Total laser time per eye was 30 seconds (on the long side); the whole procedure was...maybe 2 or 3 minutes. The only part that was uncomfortable was the cold water rinse at the end (brain-freeze/ice cream headache). The battery of eye tests months prior was more grueling than the procedure itself. It really is no big deal (and I'm a real chicken-$@1T when it comes to medical/bodily harm stuff--too squeamish to wear contacts even).
A few days afterwards, I had to keep my eyes closed, padded; the pain wasn't too bad (numbing drops). A week later, you can see fine (wear shades, everything is brighter); I had halos for a few months afterwards but they vanished. It all sounds far worse than it is.