I've heard a rumor that a lot of polishes eat away at the stitching so I have become a strong believer in olive oil. It makes leather really soft and shingy and it also smells good :P
Actually, now you mention it, that makes sense. I don't have long boots, but a friend of mine does and she was polishing them one night and went "Oh my goodness! The stitching in here is gone!" Pointing to a part of the boot. They were custom made too, not cool.
R.I.P ~ Bubbles - 25yo tb mare - 13.04.2011 ~ 8:30am ~ passed away naturally and peacefully in my arms