Do be warned that if you want to go make breakfast, you oughtta check the whole-map survey for a couple turns to make sure nobody's headed your way...and then hop onto a -2 or something, just to be safe. Minus squares don't actually hurt you all that much to camp out on; I see high-level players sit on a -1.5 or -2 instead of going into the safe area.
Also, I should clarify exactly how army strength works. Your army size changes slowly over time, but its effective strength changes faster based on what square you're on. Let's take three armies, Adam, Betty, and Chad. Each of them has a size of 1000. Adam is on a -2.5 square. Betty is on a +2.0 square. Chad is on a +0.5 square.
Adam's army strength is 2500: If you're on a negative square, your unit strength is multiplied by the square's absolute value.
Betty's army strength is 500: If you're on a positive square, your unit strength is divided by the square's value.
Chad's army strength is an unmodified 1000. If the absolute value of your modifier is 1.0 or less, nothing happens to your army strength.
Whenever you get into a fight, you always use your army's strength from the previous turn. So if Chad is on his 0.5, and he attacks Adam on Adam's -2.5, Adam wins easily. However, if both Adam and Chad move onto the same blank square (no multiplier), Adam still wins. The modifiers of your new square don't matter until all conquering in the new turn is done.
Oh yeah...and +squares slowly lose their bonuses over time. They'll be refreshed as the game progresses, but don't be surprised if your nice shiny +3.5 turns into a +2.0 over the course of many turns. If your +square is adjacent to other +squares, though, your square will drain from THOSE first before it loses its own value.