Actually, no. I run NAT on my firewall/router, and still host the services. It just takes tweaking the Linux iptables rules to run externally visible services, while still running NAT in general. Again, a "knowledge" and/or "convenience" issue, but not a technical issue.
> What do you do for secondary DNS?
I use Afraid.org for secondary DNS, but if my home link is down (hasn't happened yet...) then the service (email/web) is also down so I'm just "offline" until the link comes back up.
By "stuck behind NAT" I was meaning a NAT or 6-to-4 arrangement that is not under your control (so you can't configure port forwarding). This isn't all that common in the US or EU aside from mobile and satellite based providers (and you aren't likely to run servers off them!) but elsewhere it is more of an issue and will eventually become so everywhere where IPv6 take-up doesn't pick up fast enough.
> so I'm just "offline" until the link comes back up
I'm not sure what effects are common now (if any) but historically some services responded differently to the two downtime situations "DNS lookup worked, but I can't connect to that address" and "DNS lookup failed" - some MTAs used to be more likely to bounce rather than requeue for instance - so I always recommend topologically distant secondary DNS even for a single server+link situation. If you branch out later (for instance I currently have most things at home but a few bits external which I don't want down if my home link blips) you already have it setup so don't have the extras work to do. Also secondary DNS is required by the relevant RFCs, so if nothing else do it for that reason (I know you already do, I've added this bit for other readers should they stumble here in future).
Well many can, but far from all in the context of hosting from home. If you are stuck behind NAT at home then you can't without paying for server resource externally and that is going to be more of a problem over the coming years as IPv4 increasingly becomes a problem and IPv6 (despite recent acceleration) taking a fair long time to become ubiquitous.
> In my case, I host my own dns, ..., locally on my home connection.
What do you do for secondary DNS? Some services respond differently to "address found from name, but server not responding" than they do to "couldn't lookup name".
One particular problem I've seen reported relatively recently is bounced mail when the senders ISP replaces "could not contact DNS server to lookup address" to "I know, I'll show them my own error/adverts web page": of course the user's MTA doesn't know anything about web pages and tries to connect to the host address provided to send mail and is told to go away (either no mail service found or there is one but it refuses mail for that recipient). If you had a secondary then the lookup would pass to there so the right (but currently non-functioning) address would be given to the MTA, it would fail to connect and drop the message back into the queue for a later retry.
It is rare it makes any difference these days (many agents that were sensitive to this, such as mail servers, no longer are because it is quite common for small arrangement not to have secondary DNS and for ISPs to break DNS in the name of making an extra penny here or there) but it is still worth having an externally hosted secondary DNS host even if everything else is a single point of failure for all (hosted on one box on one link). For a small home concern it needn't cost more than ten or fifteen $/year either to run your own bind instance in a inexpensive VPS or to use a specialist DNS service.
I run most things from home too, but have external resources (a backup location and a web service that occasionally needs more bandwidth then the outgoing link at home can comfortably provide) so my secondary services sit out there with them.