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Springfield says it is ok to use +P in the XDs, just not a steady diet of it...
From what I read though, it significantly increases the already appreciable recoil, making it difficult to maintain a good shot group in a rapid fire situation.
(These are not my statements, just stuff I gleaned from the XD Forum while trying to answer the +P question for myself.)

+P means "plus pressure". In addition to the above stated over penetration issue, the round is faster. The extra pressure means the round travels faster, which means that it is not affected by gravity and wind as quickly after leaving your barrel. This extra speed ultimately means that the round is more accurate in a self defense situation where you don't have time to correct for wind and drop.