The resistor is 47 ohm, the capacitor is 10 nF
You don't need that capacitor - it is counter-productive, especially if you want to go to 1Mhz later.
You could have used some of the analog switches in the CD/HC family.
I would have used a 4.7 - 22ohm resistor to dampen, but not with an analog switch.
Now with arduino duemilanove I'm working @ 10 khz but in future I will arrive at 1 mhz or more, so don't know if this is the right switch design for HF.
A few hurdles there:
1) your buffer will give out way before 1Mhz.
2) your mcu may not be fast enough to produce 1Mhz pin outs.
Two alternatives to go to 1Mhz and beyond:
1) DDS. This approach requires additional hardware + programming. But it can generate lots of different waveforms and relieve your mcu.
2) Use a counter + resistor network. This approach requires just a serial clock (from your mcu).
A 3rd approach would be to use a memory device pre-programmed with your waveform as your own dds.