Look at it this way, the "professionals", you know the guys that build new construction houses that new homeowners usually fight with on a daily basis, usually only tile up to the cabinets in both kitchens and bathrooms, the reason for this is to save a buck.
I have tiled my share of bathrooms and kitchens and ALWAYS tile under the cabinets, mostly for all the reasons already mentioned. For me the biggest reason is the way it looks when its complete. It usually requires less cuts and if the floor is realitively flat, you can get away without using any (or very little) moulding to cover up the cut ends, it's a much more professional look. Remember to take into consideration the added hieght, although minimal, that the tile board and tile will add to the countertop (for backsplash, outlets, etc)