Good question, simple answer: The lower the pin count, the better it is.
In the audio synth application I'm currently working on, I need the pins 0 & 1 for Midi In/Out purpose, and also need four analog inputs for control Knobs and so on. Add to this three Leds for Synth operation purpose (gate + lfo rate + general purpose), four buttons for operation like preset managment and edition, and make the breakout:
2 + 4 + 3 + 4 = 13 pins, with 9 being discretes.
With this basic setup, I have no room for Port dedicated 8 Bit DAC on a Uno board.
Then, in the future I plan to use a MCP4921 as a DAC. This will lead to better results, so using a homemade SPI DAC in this case is the best way to anticipate design evolutions.
However, as I mentionned on my blog, I started using a rough 6bits DAC on PortC with great success... except for dynamic range of course 