Sorry a little slow about responding. Actually forgot about this post thanks to getting involved in several other things over the past couple of days and didn't even catch this post as I was looking through the message board and thankfully the weekly email caught me and reminded me about this post.

I haven't noticed any top heavy conditions at all. If you remember to pack the pack like you do for long distance hiking, heavy items on the bottom, then their is no reason you should see any top heavy problems. Think about it, why would you. Instead of having the gear attached to the sides of the bike you have the gear directly sitting over the center of the bike. The weight may not be as close to the ground but it is attached directly to the body, not the bike. It makes bike handle much easier. One bonus I found out in Hagarstown, MD, if you happen to run into a situation like I did, traffic jam he!! and a town with high curbs, you don't have to worry about dragging panniers(pain in the arses) on the curbs and you have a lot more room to lean to bike to get around semis that are parked in the road waiting for the traffic in front of them to move.

I will agree with bradtx, if you have the backpack fully loaded to the top it does make it a bit more difficult to see around the back side, then again if you are like most tourist you use a mirror so their is no reason to have to look behind you, just look in mirror.

One thing to consider also about using a trailer, how much does the trailer weigh? The extra weight to haul the backpack is more weight your going to have to carry up every hill that you climb.