There's an interesting piece by Laura Miller on Salon about present vs. past tense in fiction. Evidently judges of various literary prizes are up in arms about the present tense. Too much contemporary literature is written in present, they say. It's too trendy, to MFA-y, and too wishy-washy--i.e. unwilling to commit to stating that something actually happened. Present supposedly creates a greater sense of unreliability, which I guess MFA types (especially girls) prize. The judges long, as it were, for the past.
As I am always a step ahead of the herd (usually because I am lost and have wandered into a farmer's field), I have already transposed my novel from present into past. I don't think it was because it seemed too trendy or wishy-washy. I wanted the story to seem more like a tale, a bit more mythical. If anything the past tense seems more flexible in the did-it-really-happen department. Present tense consumes the storytelling; there is no perspective, nothing outside the present moment, no wiggle room to say, wait a minute... Whereas the past could be someone spinning a yarn. It could be a tale told a thousand times already, by a thousand idiots, or liars, or tricksters, or people with poor memories. At the same time, it does have this oracular quality, but I think, in this day and age, that quality can be usefully played with.
Past also allows you to move closer to and farther from the action at will. There's room to insert reflective passages, but then you can dive back in and get really close to what is happening, for all intents and purposes, now.
As Miller says, if the writing is good, you'll get caught up in the story either way. You might not even notice the tense unless the writing is bad in other ways.