Good point Ray. There is the core Tomato functionality, then the “bonus” (??) features like the Bit Torrent and NAS/Media Server that are built into the TomatoUSB mods, and then any of the hundreds of available Optware add-ons. Using Tomato in a production environment will likely require the owner to resist using or adding many of the cool features as they could compromise its stability/security. That said, you could argue that it is no different than using a regular Linux server in a production environment – if you must load non-production software (for testing or entertainment) do it on a separate machine.
As I said, I have used 2 Tomato routers as firewalls to my small office (with servers behind) so I don't have to worry about scalability. They connect to separate Internets, so if one fails then communications will flip to the other router. The system has been extremely solid for 3 years but I don’t use the routers for anything else besides fire-walling (NAS, Port Forwarding). My job doesn’t depend on it (I wouldn’t fire myself) but my business does depend on reliable network communications and I would lose customers if it was compromised.
While Tomato (and TomatoUSB) has been stable, my main concern is about using it as a firewall since there may be some code that is out of date and can be exploited. Or alternatively, some new Linux code (iptables, routed, bind, dns) may have been integrated into the mod too soon and it may be susceptible to exploits. Do we know how “safe” the base Tomato and some of the Tomato mods are in this regard?