Hi,
Regarding the value of the feedback resistor, it should be there from a DC but should not be there from an AC point of view.
For DC, the smallest value depends on how much dissipation we wish to make in the active device, and for AC the smallest value depends on causing the least negative feedback possible at the oscillation frequency.
For DC, the highest value depends on the active device input and output resistance, and when you bridge the two with the feedback resistor, it should be able to transfer any DC voltage changes between the two (i.e. keep the operating point at the half VDD value). In case of a TTL gate/inverter this value is a few kiloOhms but for a CMOS or HCMOS gate/inverter it can be in the MegaOhm range.
(Note: when a few kOhm is needed the feedback resistor must be made from two equal value resistors in series and use a capacitor from their middle point to the gnd to prevent (short-circuit) any AC feedback via the low value resistor. In case of a CMOS gate this is usually not problem with the MegaOhm (5.6-10MOhm) value feedback resistor, though the same capacitor shunt still can be used in need of using two series resistors.
Regarding the role of the 'damping' resistor: One role is indeed to reduce crystal dissipation (it is actually in series with the crystal), another role is to help create additional phase shift in the oscillator loop, workin together in this respect with the capacitor which is connected to one of ends and the gnd.
See additional info at two links on these:
**broken link removed**
http://www.fairchildsemi.com/an/AN/AN-340.pdf
Regards
unkarc