I've been rocking my first gen on 3.1.3 for about two months now exclusively after selling my 4S. The back of my phone is somewhat worn out and I have had to do a bunch of internal surgery on it over the past couple of years but it's still kicking. My 5 is scheduled to arrive today so this will be going back into semi-retirement tonight. I don't ever fully put it away I leave it on wifi and play with it every couple of days to keep it somewhat active.
Like I saw somebody else say, I've never had a screen protector on this phone and I don't have a single scratch or blemish on the front. The phone does get frustratingly slow at times. I have virtually no apps on it (and couldn't if I tried), no music, and maybe only 30 pics but it will still sometimes bog down/freeze so much that I can't even answer an incoming phone call. I have to restart it several times a day.
The crazy thing is that even on EDGE speeds you get used to it. I still browse as I normally would (albeit slower), but I have to use the mobile web versions of apps instead of the actual app since this phone isn't supported (Twitter, Facebook, etc). In fact I'm posting this from the phone! I only get about 3-4 hours of usage time total even with a new battery - granted though I rarely talk on the phone so that's mostly web/data usage. Really, the biggest thing that's lacking is no MMS and the camera is really bad in anything except bright daylight.
And, oddly, I have noticed that my wifi signal on this phone is much much stronger than my 4 and 4S were.