I have a 1.8in drop, since i run 40 series tires, i kinda wish i went with a 2.0 drop, definetly. BUT BUT BUT make sure you put in new shocks/struts and a camber kit AT THE TIME of spring install. You'll save on install costs majorly, and it must be done. I've already camber wore out my rear tires to all hell and my ride is majorly bumpy on stock dampers.
18 is a very big wheel for the focus, 215/35/18 tires are really really thing, they're begging for you to hit a pothole. i wouldn't go more than 2.0 on the focus though, 1.5-2.0 is perfect depending on your tire size.
I went 1.5" with Steeda and KW dampners. It leveled the car out very nicely, got rid of the "high" ass end. I went to 205/50/16 tires ( plenty big enough for me) and I believe it looks good and gives a nice but firm ride.
A two inch plus drop will really stress stock shocks and struts (dampers). Such a drop will significantly shorten a stock dampers travel and you will either be riding on the bump stops or be bottoming the damper. Neither is good. One good hit will damage the valving mechanism and your damper will be toast. You should seriously consider using a damper that has a shortened body (to maintain adequate travel) with that amount of drop.
I got the eibach 2" front and 2.25" rear joined with one of the best shocks on the market, Koni Yellow fully adjustable Shock. The result, absolutely horrible. I'm not sure why, but it feels like the shock is not only hitting the bump stop but bottoming out completely. I totally do not recommend getting the Sportline kit unless you get a short shafted shock.