However, people that love the woods, really love the woods. It is such a unique location and can really make you feel like you are up in the mountains somewhere (go get that feeling anyplace else in OC). Usually the homes that may be on stilts are built that way because they back to one of the ravines. Those homes, because of their views, are often the most desirable and priciest of the woods homes.
As has already been said here, having a competent physical inspection is always of utmost importance on any home purchase. If a good inspector (or your Realtor for that matter during their visual inspection) sees any red flags such as cracks in the walls or doors that won't stay open etc. they will possibly recommend a further inspection by a geological or structural inspector. In fact, if a buyer in escrow is concerned even without seeing any obvious stuctural or geological problems, they can always pay for a structural/geological inspection just to set their mind at ease.
You need to have a good home inspector evaluate whether or not any particular house is well-built and won't slide down the hill. There are many homes in the woods in Lake Forest with good foundations, or well-built on stilts, so you just have to consider the location and the quality of construction individually.