Some rules I may try or at least wait to get the book to decide if the particulars will work (DR is one of these, but it is looking more and more doubtful.)
For some other rules, the whole issue is backwards compatability and conversions. If I get to the point that I can be "trying them out", then the point is moot. The rules should serve the game, not vice versa.
Some rules have flavor considerations and/or have design philosophies behind them which I consider fundamentally flawed. Paladins summoning warhorses, for example. The whole "be at your best in the dungeon" philosophy does not fit the general feel of my campaign, and it threatens to pidgeonhole D&D into "dungeon bashing" as bad as some critics perceive it.
3.5 has many changes I consider essential. But this design team has not earned my respect to the point that I feel I can plop changes into my game sight unseen. Essentially, I am seeing 3.5 more as a supplement than a new core ruleset, and like a random d20 product, I will use what works and ditch the rest.