For the most part, Spring Training stats should be ignored, just like Spring Training standings. But there are at least three situations where its worthwhile to pay attention to Spring Training stats:
1. To see whether players returning from injury will be effective. Particularly with pitchers, you can tell how they're doing by looking at their K/9 and K/BB. Just make sure to ignore stats like ERA that have more variance. Good examples in this category this year will be guys like Dotel, Gagne, and Isringhausen.
2. Look for young hitters with MONSTER numbers. Not just good numbers, but numbers among the best in the league. Research has shown that guys who have a Spring Training slugging percentage more than .200 better than their career average will tend to improve their regular season stats. Andruw Jones right before his breakout season was a good example.
3. See how players fighting for jobs are doing. You're really trying to look at this from the perspective of their managers, many of whom put too much stock in Spring Training stats, despite the small sample size. This may be players trying to stick in the majors, fighting for the closer job, or fighting for an everyday spot in the lineup.
The best place to get Spring Training stats is MLB Spring Training Stats.