I started with a Canon AE-1 back in the late 70's and used it up until the late 90's. I was having more and more trouble focusing as my eyes started to get older. Not really a problem for still life, landscape, macro, etc. but was a real problem for people/travel photos.
The last straw came on a trip to Italy. We were in Rome at the colosium taking the usual record travel shots but I always keep an eye open for something different. All around were the usual guys dressed up as gladiators and the like where you can pose the wife with one in front of the monuments, colosium, etc.
I happened to notice one in an alcove in full regalia on his cell phone next to a statue. I thought, "What a fun shot!" Well, I coudn't focus fast enough with my older eyes and lost the shot. That was when I decided I really should go Autofocus.
I looked long and hard and ended up jumping in feet first with a F5. I now have that F5 as well as an F6 and am very happy I choose Nikon. Sold the AE-1 to a good friend and have never looked back.