You've touched on one of my favorite--or should I say least favorite--subjects. It seems the standard traffic pattern has been expanding at an increasing rate lately.Unfortunately, the situation you describe is very common. One pilot flying a wide pattern can throw off the entire parade. Although engine failures in the traffic pattern are rare, flying a reasonably tight pattern makes good sense. It keeps the traffic close to the airport, makes more efficient use of the available airspace, and cuts down on noise complaints from the neighbors.
Unfortunately, unless you're in very clear communication with the other pilot, you should follow the airplane ahead of you. Being inside another airplane in the traffic pattern isn't a good idea. Good airmanship means being able to adjust to changing conditions.
I don't encourage pilots to discuss flying technique over the CTAF, but perhaps you can drop a hint by saying something like:
"Podunk Traffic, Cessna 123 is on the upwind runway 36, and I'll be flying a tigher pattern on the next circuit. Podunk Traffic."
In the meantime, you can encourage folks to review the AIM (4-1-9), the Airplane Flying Handbook (FAA 8083-3), AC 90-66A
If you're an AOPA member, you read some of these documents (and few other handy references) online:
http://www.aopa.org/members/files/ac/ac90-66a.txt
http://www.aopa.org/asf/safety_topics.html#airport
http://www.aopa.org/members/files/pilot/2001/noise0108.html
http://www.aopa.org/members/ftmag/article.cfm?article=4082
http://www.aopa.org/members/files/pilot/1995/pc9512.html
http://www.aopa.org/members/ftmag/article.cfm?article=471