One of the bigger problems I have with writing semi-period pieces (i.e. Steampunk set at a particular societal level) is that I have to find slang words that fit the story. Things like the word "Hey!" and "Oi!" might not work as exclamations to get someone's attention because they sound too modern.
So I end up trolling the dictionary for words that are at least as old as the time period my stories roughly take place in. With CALLARION AT NIGHT, that means going for Victorian England. With SON OF MAGIC (my completed MS), I have to aim for either creating my own words or using ones that have etymologies at least back to the 14th Century. That way I can be certain of the word not pulling people out of the story.
This can be crazy-making sometimes, especially when my crit group finds a word and says "That's too modern." And then I go back to the drawing board (mind you, I adore my critique group -- they're a talented bunch that have laser-guided eyesight for each class of my traditional errors. And they put up with me taking the proverbial red pen to their works. So I'm happy.).
I know I'm not the only one who has this problem (Gary, I'm looking at you), but I'm curious about how other writers of historical fiction/fantasy deal with the word choice issue.