Too much trail can lead to a bike that won't initiate turns at speed or easily get pulled back out of turns.

My old school bomber mountain bike is that way but Lord is it fun in a straight line!

More trail increases the lever arm that keeps the front wheel straight and hence the force required to turn the bike. Turning the bar also lowers your center of gravity slightly. More trail increases the effect and hence the force necessary to straighten the bars back up. Less offset is also a shorter wheelbase. A shorter wheelbase can improve low speed maneuverability.

Overall, I liked what changing the fork rake from 45mm to 43mm did for my road bike. I think a 5mm change would've been too much though.

There are just too many factors to be covered in a sentence or two. Check out the chapter on frame geometry and bike stability in Zinn's Cycling Primer. http://www.velonews.com/media/Block40.pdf There's also this http://velonews.com/article/9314 with some additional comments on shimmy.

If you decide to try it, leave the steerer cut 15mm too long for a while so you can sell it easier if you want to switch back. Taking the loss would be tough, but it would be worse if the fork were left with a steerer too short to fit on anything else.