In the recent case of R v Hamilton, 2011 ONCA 399 the Ontario Court of Appeal considered the issue of interventions by the trial judge during a long and difficult murder trial. Two of the appellants argued on appeal that various interventions by the trial judge undermined the fairness of the trial [paras 35-42].
In dealing with this ground of appeal, the court first offered the following succinct summary on the approach to this issue:
When evaluating interventions by a trial judge, the fundamental question is whether the interventions led to an unfair trial: R v. Valley (1986), 26 C.C.C. (3d) 207 (Ont. C.A.), at p. 232, application for leave to appeal dismissed,  S.C.C.A. No. 62. This assessment is made from the perspective of a reasonable observer present throughout the trial: R v. Stucky (2009), 240 C.C.C. (3d) 141 (Ont. C.A.), at para. 72. Isolated expressions of impatience or annoyance by a trial judge as a result of frustrations, particularly with counsel, do not in themselves create unfairness [para 30].
After reviewing in detail the impugned interventions, the Court of Appeal offered the following quotable quote:
At a time when we are concerned about the increasing cost and length of criminal trials as well as their drain on resources and the pressures they bring to bear on the administration of justice, appropriate trial management is to be encouraged, not muted. In a case of this complexity and size, a good deal of deference is owed to an experienced trial judge who lived those dynamics for many months; dynamics that must have impacted on his decision to intervene from time to time. A microscopic analysis of interventions by a trial judge in large cases such as this should be avoided [para 49] [emphasis added].