During a recent discussion of pattern entry procedures I mentioned that I
had submitted the question to the O'Hare FSDO. After being forwarded about
five times in the FAA beauracracy, my email eventually reached Inspector
Sandra Boerman, who responded thursly:

The FAA guidance for traffic pattern entry procedures comes from the AIM,
AC 90-66A (Recommended Standard Traffic Patterns and Practices for
Aeronautical Operations at Airports without Operating Control Towers), and
14 CFR Part 91. Also, there is a video called "Operations at a Non-Towered
Airport" by AOPA that is very helpful. 14 CFR Section 91.126 does not
prohibit 45 degree pattern entries. When you are on the 45 degree entry, you
are not in the traffic pattern; therefore, a right turn to downwind is not
violating 91.126. The traffic pattern is upwind, crosswind, downwind, base
and final as defined in the AIM. 14 CFR Section 91.126 states that all turns
must be made to the left unless the airport displays approved light signals
or visual markings indicating that turns should be made to the right.

According to the above guidance a 45 degree pattern entry is the recommended
procedure for entering a traffic pattern at a non-towered airport. However,
for those pilots who choose to execute a straight-in approach, maneuvering
for and execution of the approach should be completed so as not to disrupt
the flow of arriving and departing traffic. Disruption of the flow of
traffic could be consider careless and reckless behavior.