.local domains conflict with Bonjour/Avahi
If you have your domain set to local in pfSense and you have clients using Bonjour/Avahi on your network (if you have any Apple machines/devices on your network then Bonjour is being used), then those clients will not be able to resolve any local hostnames (i.e. pfsense.local) because Bonjour will intercept any .local name requests and attempt to handle them itself. The solution is to change the domain in pfSense to something other than local. Mac OS X 10.6 will work correctly if you simply add an additional label to the domain: i.e. mynet.local. Older versions of Mac OS X and Linux systems using Avahi will likely only work if your domain does not end in .local and/or require additional configuration.
If you're trying to debug this problem, affected machines will have no problems resolving .local hostnames via dig and nslookup, but name resolution will fail via more indirect methods (web browser and other utilities that go through the full hostname lookup procedure). You will still be able to access the service directly by IP.
pfSense devs: It might be a good idea to change the default pfSense domain to something other than local or include a warning.