Currently about once a week. The impact on our finances is pretty close to zero. We found a local Mexican restaurant that runs a special on Tuesdays. Chips, salsa, water, 2-3 tacos each, and the best Pina Colada(shared) we've ever had for $14. Once or twice a month we order pizza, mostly for the kids. Pizza joint nearby has excellent extra large pepperoni for 8 or $9. LOTS of large delicious pepperoni. I'm not sure we could make it that cheap at home honestly.
I'm 100% in the camp that it doesn't make any sense to look back one day and wonder where all the money you made went, and realize you ate it all(eating out). It's an expense I definitely like to keep firmly under control. I do prefer to eat at home most of the time.....It's hard to enjoy a meal out that isn't at least a reasonably good value.
For my birthday, I asked for a meal at home. I preferred it greatly to a $200+ family eat out splurge. Maybe its a mindset that eating at home is not a punishment, and eating out isn't necessarily always a reward. But if I feel like going out for a taco after work, I'll do it, find a good value, and enjoy it 100%.
I've seen people push frugality to the point that it detracts from quality of life for a negligible amount of money. Visiting family in Germany. After a long international trip, we made the mistake of having a long drive to our destination, picked up by family. We sat in a 2 hour traffic jam on the autobahn....hot, miserable day. Rather than roll the windows up and use the A/C to be comfortable in a miserable traffic jam, it was windows down, no A/C, ignition off every time we stopped for a few seconds. I would have gladly paid the $1 or $2 for gas to be less miserable. Sorry, bit of a tangent. /endrant.