Yea, all the responses are correct. I think the plain answer to your question is that a lift will not void the entire warranty flat out (there has been legal action on this, and I too believe there is legislation protecting ones right to use of aftermarket parts, including lift/lowering kits, will go check and try and get back on this)...Talk to the dealer you plan on using for repairs though.
That's the cut and dry. reality is, wheeling or not, if your lift causes problems, and the linkage between lift and problem is obvious, you are not covered. Nor are your lift parts covered.
EDIT: ok, some additional interesting info.
The Magnuson-Moss Warranty-Federal Trade Commission Improvement Act of 1975 lays out your automotive modification rights under federal law. The M & M act says that the manufacturer must state clearly what you can and cannot do to your vehicle and remain under warranty. It also states that it must be clearly listed under a heading entitled What Is Not Covered, or words to that effect. M & M states that the dealership must explain how the modification caused the problem. If they cannot explain, or their explanation does not make sense, you've got them. They have got to comply and honor your warranty