I have been on the forums, tinkered with the box, and talked to tech support and have the following problems. All in all it is a very nice product and hopefully addresses these issues but until then it just isn't really ready. It is just too inflexible.
1. Administrative Control - I have seen this touched on in a few places and it seems like it may be addressed. It would be really nice to have more fine grained control over a number of aspects. Spam filtering, spam learning, dhcp settings, routing, filtering, etc.
2. DNS/Split DNS - It would be nice if this ran a full fledged DNS service. Let the user choose if they want to host zones or only do forwarding. The really nice one would be if split DNS was enabled the same way Sidewinder does.
3. SMTP - Same deal, as I understand the only way to use this is a transparent proxy. I would rather see this being able to be used as a full fledged SMTP server for small/home business and a true SMTP relay for larger environments.
4. HTTP/HTTPS - Running the management tools on nonstandard ports would be better so it is possible to run a web server on the device itself. Again this would primarily be small/home business use.
5. VPN - I don't even know where to begin on this. No IPSec so my only option is to tell every other site that I need to connect with to ditch their expensive enterprise gear from Cisco or Sidewinder and buy Untangle so we can build secure tunnels. That is a quick way to get yourself laughed right out of a business deal. I was also told there is no VPN passthrough so not only can I not put a normal IPSec device behind it, I can't use VPN clients to connect to other sites.
The VPN structure alone pretty much excludes it from any real larger or enterprise functions and the lack of fine control is going to turn away places that have real IT administrators around. The lack of flexability in consolidation of services moves it out of the home/small business where the lack of control isn't so much of an issue. So it really can only serve a very small subset of business needs. The product definetly seems like a good start, but it needs some work to be able to be very functional outside of a very small scope of networking needs.