Charles:
Here are some references that will help to clarify the point.

http://homepage.tinet.ie/~ei9gq/tx_circ.html
In this above reference scroll to the Figure 1. Notice the design using a power limited CMOS unbuffered inverter. Feedback resistor is 22M as opposed to 510
and the inverter output is limited through a 330K resistor before being applied to the crystal.

http://www.act.co.uk/techinfo/...y_txt.html
This reference from a crystal manufacturer indicates that one of the factors of crystal aging is overdrive. Scroll down to the paragraph on Drive Level.

http://www.semiconductors.philips.com/acrobat/a...7090_1.pdf
This reference from Philips gives a lot of information on crystal oscillators. Scroll to page 10 (Section 2.4) for a good discussion on crystal drive levels.

http://www.statek.com/new/pdf/tn30.pdf
This link takes you to the Statek Tech Note 30 which provides a rather analytical look at oscillator designs and crystal characterics.

http://www.saronix.com/Document_...n-0305.pdf
The SaRonix crystal manufacturer has a nice application note covering crystal oscillator designs.

Note all these were located on WEB via a simple Google search.

Michael Karas