Do you say something to the person in question? Do you adjust things on your end (I seem to recall it's possible to override the personal settings and force all LJs to appear in your chosen mode)? Cut 'n paste cut-tagged entries into a notepad file to read them? Just skip the entries and don't worry about it?
Conversely: if someone found your journal's settings unpleasant to look at, would you rather they said something so you'd know, or would you consider it rude if they voiced their opinion?
I know I'd rather know. But then again, I've never bothered to change the style on individual entries, so my chosen style would only be an issue for people who read directly from my journal, as opposed to from their friends list. On the other hand, I recently switched styles on unfinishedtales, and have been wondering since then if the new style causes trouble for readers (it seems to scroll slower to me). Aha, and Lut just noted that this is a problem for him, too. Methinks I need to switch it off. Hmm. I'm thinking that if you want people to tell you if your journal style is annoying, you need to ask them directly, rather than expecting comments if it's a problem.