A few years ago I bought my wife a Specialized Ruby Comp. She had done some riding before that on an older ill-fitting hand me down with DT shifters and thought she'd enjoy a "real" bike, so i jumped in. Since I bought her's new, I actually spent more on it than I had on my own bike. My theory being as follows: Spend less on a crappy bike for your wife fearing that it won't get used anyway, and she'll resent the fact that hers is heavier than yours, and doesn't look or shift quite as nicely etc....and guess what, self-fulfilling prophesy. The bike hangs in the garage for years, and is eventually sold off. But buy her a bike as nice as yours, and she'll take it seriously, have no barriers to excel and will have a better chance of learning to truly enjoy it.
Well, for me (us) my theory paid off. Her school schedule over the first couple of years kept her from putting huge amounts of miles on it, but I always made myself available to ride with her when she did have time, even missing my own group rides at times to ride with her. This past year she's had more time, gotten in far better shape, ridden lots with me and some without me, and even done a handful of races. She's joined me many times at the local crit practice, and has really discovered a love of competitive riding. We've both joined a great local team and plan on doing more racing in the coming year and likely beyond. Oh, and in addition to riding on the weekend with me, she's even been commuting to work most days and loves it. Hooray bike-commuting.
So don't be discouraged by the stories of failed attempts to get wifey to ride. Just be deliberate and smart about priorities. Also don't fall victim to the habit of riding 10+ yards OTF while "riding with her." Ride WITH her or behind her when necessary if it helps. And
for buying an equivalent bike for her. I'm certain that it makes a significant psychological difference.
*edit* Oh, also NEVER, and I do mean NEVER try to combine your training rides with your rides with her. It simply will not work.
Best of luck.
-Jeremy