Mabd, here is the datasheet: http://www.ortodoxism.ro/datasheets/microchip/21388b.pdf
Those parts are simple, robust DACs. I always used them without problems.
Caveman, if for example one wants 100k samples /second then PWM simply won't cut it, you must set the PWM for at least 4 times the sample frequency (8 times is even better) so you won't have hiss in the signal. No PIC can produce such a high frequency PWM at more than 4bits precision. This is a clear case for DAC's.
Let's assume you want to output a 16kHz wave file. You must put the PWM for 4x that frequency to still have 8 bits precision, but you will still have a high pitch hiss and if you filter that out than you loose the upper freq. part of that wave file. If you try 8 or 10 times that frequency you won't get 8bits precision anymore. Now just think of a 96kHz wave file...
On the other hand if you use a 8bit DAC then all your problems are solved and you just have to pump those 8bits at the required frequency to get a clear and crisp sound.
(a pic 18F with a built in DAC would be great! somebody should hear this at microchip - how hard would it be to put an 8 or even 16bit register and 16 or 32 100k and 200k resistors in there, tied to a pin?)