hey ... I have an Early 08' Penryn MBP as well and after hours and hours of reading reviews, searching forums, etc... i bought the BSE "Best Skins Ever" film, fraction of the cost of the InvisibleShield which is exactly like InvisibleShield without the lifetime warranty and without the liquid solution (soap+water) and squeegee. Google: Best Skins Ever. In addition, I purchased a speck hard case on discount since my model is discontinued for around $20 from a store called Futureshop (a best buy company here in canada). Speck has a current 50%-off all the old macbook pro cases, I didn't buy it from Speck as my shipping came up to around $30. I will be installing the "Best Skins Ever" transparent shiny protection, I will let that settle for 24hrs then I will cover my machine with the speck hard case.
Last night I installed my brothers' Invisible Shield from Zagg on his 3g iphone and it was not an impossible task but very annoying and frustrating, as I feared getting water in-between the cracks. I am already dreading the installation of the "Best Skins Ever" invisible protection after reading the above comment about the apple store genius finding water traces inside the machine and canceling the warranty. I would not be able to handle that kind of stress if my warranty becomes void. I depend on my machine too much. The reason I bought two types of protection, according to my little research, I have found that dust gathers inside the speck thru and those little tiny dust particles end up scratching the surface of the macbook pro. So my mini-strategy is to clean my macbook pro's surface of any dust then install the shiny "Best Skins Ever" transparent film (eventhough i despise the extra shine), this way, if dust particles slip-in under my Speck case, then it wouldn't scratch the actual surface of my macbook pro as it will be protected by the "Best Skins Ever" transparent film. I also purchased a zcover keyboard skin.