For most folks, Disc Brakes are a gimick that they don't need.
BUT... For those that ride a lot in wet weather/Rain and such I think that Discs
can be an added benefit to those folks. It is very hard to beat V-Brakes. I try and ask the customer enough questions about how and where they ride. There are certain factors that make V-Brake or Discs more desirable. The other factor is adjustments. Some folks will not pay attention to pad wear and pad adjustment with disc brakes. For these folks, V-Brakes are a better choice. For customers that tinker and have the aptitude to maintain their bikes, or those that regularly bring their bikes in for service, then Discs may be a better choice.
For myself, I am building up my first bike with Discs. I built it from the first part with discs in mind. It's been a soggy spring this year and our roads around here still really do not have the salt fully washed off of them. But, The frame and fork on this bike still have the canti braze-ons so I could switch back if needed.
Chris