Fannie Mae put an exclamation point on the housing rally with last week's announcement of its largest-ever annual profit. The news comes soon after Fannie's cousin, Freddie Mac, announced its own record high. These results may seem like cause for celebration after years of losses at the two taxpayer-backed mortgage giants. But they also underscore the urgent need for reform to ensure that the next real estate boom doesn't end as badly as the last one.

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It's certainly good news that the very long housing recession is finally...