For most of these things, I prefer one way over the other(s) and I stick with that in all my writing. Though sometimes, I use a hybrid. For example, I will mostly use British spellings (colour) but will use American ones when writing for select words (standardize). Sometimes I switch between the two systems, depending on what I'm writing. Here, for example, I would probably write 'programme'. For a university assignment, I would probably write 'program'. On the Internet and in programming, I have to use 'color' instead of 'colour' all the time. It's not that hard to switch, though.
There are two style choices, however, I'm not so sure about: writing times and writing titles. And my not sticking with one convention is starting to get on my nerves.
I tend to switch between two writing styles when writing times. I use uppercase 'AM/PM' when writing specific times, such as "the movie runs from 11:30 AM to 1:15 PM". But I use the lowercase 'am/pm' when writing times within flowing text, such as "see you at 3pm". In my opinion, "see you at 3:00 PM" reads too formally.
My problem, however, is that I am tempted to use the lowercase 'pm' notation all the time (ha ha, a pun!). I know that's what some writing style standards use and I am tempted to adopt that all the way as well. Maybe I will. Meanwhile though, I'm stuck in the middle.
And then there are titles of published works. Which do you think is correct: "I watched 'Transformers' on the weekend" or "I watched Transformers on the weekend"? Both are, actually. It depends on whether you're using rich text (in which you can use italics) or plain text (in which you can't).
At one level, I want to use plain text all the time. That is, I would write the movie title within apostrophes. I would also write things like: "The movie was *really* good" instead of "The movie was really good". By doing this I don't have to worry about people using plain text e-mail clients or about any font conversion problems (though that's more for smart quotes in word processing programmes). It's also pretty clear in the first version that I am emphasizing the word 'really' so that's not much of an issue either. For the most part, though, my choice is determined by the context. If I don't know which e-mail system someone is using, for example, I stick with plain text. When I know someone uses rich text, I will use the italics (and boldface and bullet points, etc.).
For blogs such as this one, though, things are different. I can use italics all the time with no problems whatsoever. Why don't I, though? Well, primarily because I'm a bit of a computer snob and I think plain text is the 'classic', format independent, platform independent way of doing this (i.e. it's cooler...in a geeky kind of way). And if I switch over to using italics all the time then...well, then, I should start doing that everywhere else too (i.e. in my e-mails, documents, etc.). Right now, I'm stuck in between the two and am, therefore, somewhat inconsistent. Even on this blog. And it bugs me.
By the way, last year I finally resolved the quotation mark vs. apostrophe issue that I used to have. I now use apostrophes to emphasize words or phrases. That's why, a couple of paragraphs ago, I wrote 'really' instead of "really". I then use quotation marks only for direct quotes from speech or text. You might, when you read this, be thinking: "Well, duh! That's the way it's supposed to be". But please understand that I come from a computer programming background where only single characters are placed within apostrophes. All other text is placed within quotation marks. It took me a while to finally get that out of my system!
One way to resolve my dilemma, of course, is for me to choose a style manual I like and then stick with it. Nadia, for example, follows the Chicago Manual of Style (CMS). I follow that for the most part as well. The Oxford Manual of Style is another popular one and most publishing houses (academic and otherwise) generally have their own, internal, published or unpublished writing guides. Of the ones available on the web, the two more popular ones are the Economist Style Guide (though that's mostly for magazine and journal research) and the Wikipedia Manual of Style (which is primarily an encyclopaedia style guide).
I mostly follow Chicago though I do take elements from other style guides. At least I think I do. I havent actually read all of CMS to see whether I'm following it or not! What I do know, though, is that, in the am/pm vs. AM/PM debate, Chicago chooses the latter. And we're back to my indecision.