I suppose it's possible that you never ran into the campaign save issue, since it seems random. And if you always finish levels in a single sitting, obviously it wouldn't affect you. In my case, at launch, campaign saves were failing more often than they were working.

I suppose it's also theoretically possible that customs were working fine for you since day one, although it's hard for me to believe, considering that I recall literally spending half an hour or more between each game trying to bring parties back together. (That situation has been greatly improved; seems like joining a party usually works out in 1-3 quick tries now, and made more convenient by a usually-working active roster.)

It's not possible forge has worked without issue, though, unless you're only talking about H2A. Forge for Halo's 3 and 4 is literally missing features, and in Halo 3's case it's fairly catastrophic, preventing people from setting up anything for objective game types. Forge is stable*, but the mode is certainly not providing the functions that it should.

*And considering everything else, the file system seems to be surprisingly functional. It feels like there should be more slots for things, but it's responsive and generally seems to do what I expect it to.