Merlin Missy has been active in online fandom since 1994. She likes fanfics with plots and happy endings. Once upon a time, a well-known fan community received a Cease and Desist letter for the contents of their website and comm. In this particular story, it happened last week, the website was Jensenvention.Com, and the people involved are still upset about it. I am not here to mock their pain. I am here to use them as an example. Famous people are aware of the Internet. Celebrities we adore and cherish have websites. Authors we stalk admire have blogs and Livejournals. Wil Wheaton posts about poker and his kids. We live in an amazing era, where a handful of keystrokes may separate you from the person you think is the most awesome human on the planet. As my friend Amilyn puts it, we're living in the future. And so are they.
Your favorite celebrity, unless s/he is posting directly to his/her own blog or LJ, probably has a person (or people) whose job it is to monitor things posted about him/her online. If you run a fan website with pictures and sightings and interview snippets, the celebrity's web rep probably has visited your site to make sure none of the pics are unauthorized nudes. If you write Real Person Fanfic (RPF / RPS for the slash variety), the web rep may not have read it but probably has dropped by your blog or website to take a look. Ceiling cat is taking notes.
If your favorite celeb does operate his/her own blog, then you can chat directly with the person you admire, for both the good and the bad things that entails. You can tell him/her exactly what you thought about the symbolism of the lights and shadows in scene four and how that relates to the broader character arcs and themes of the second season. S/he may then kindly (or not) let you know just how much crack you're on wrt your theories. If you're eloquent and persuasive enough, you might even be able to affect later developments in the series, although it's unlikely and going into a conversation with a celeb with that in mind is more likely just to piss him/her off.
Sometimes? They're really pissed off about it. A particular writer I'm thinking of recently bemoaned how creators are seeing complaints online about the directions of their series and the fates of particular characters. The truth is, as fans we've been complaining about the crud that goes down on our shows long before we ever had a way of communicating that effectively to the people in charge, just as we've been praising brilliant plot twists and character details without ever finding a way to tell those same creators "Thank you!" A friend at a con ran into a television writer whose work she admired, and immediately gushed over a line he wrote for Zorro: "Love fries a man's brain like a crisp tortilla." The writer was flabbergasted that my friend a) knew who he was, and b) well enough to quote his work at him. But we're fans, and frankly, we're like this all the time. The Internet has just made it that much easier to share.
What does this mean for us? Well, if you want to go all Heisenberg and stuff, knowing for certain that we're being observed right back generally changes the way we post. For example, when posting on a bulletin board frequented by the showrunner and writing staff of your favorite series, you're going to be more circumspect in your analysis if a particular episode, in your opinion, sucked donkey balls. It's not polite to tell someone that their hard work is the literary equivalent of dog diarrhea, and certainly you can't go around posting those words and expect the writer in question to be happy with you afterwards. Your "telling it like it is" is their "acting like an entitled asshole" so if you go in there with guns a-blazing, expect not to be invited back. Simple logic.
Now extend that logic. If you have a website dedicated to a particular actor, writer or series, again the web mod will be dropping by. If you continue to post that Actor A is a fat loser and Writer B is a talentless troglodyte, the web mod is not going to think kindly upon you. Nor are the fans of Actor A and Writer B. (This may be your intention. Tweaking other fans is a risky but occasionally amusing pastime. Ask the Jensenvention folks.) You don't have to let that stop you. Your website and your blog is your space to use as you please, as long as you're not violating any local, federal or international laws. Freedom of speech doesn't mean you have to put up with trolls, it means the trolls are free to found their own blogs and websites to say what they think. But your audience, both friendly and not, is there, and you need to be aware of their presence, even if you don't care.
The celebrities are out there. Also, they're just like us only a bit more famous. Insults that would hurt you to read about yourself will also hurt them. Creepy stalker-like behavior like posting their home addresses and squeeing about driving by their mom's houses will in fact creep them (or their appointed representatives) out. And so on. If you post your sexy fantasies about John Barrowman, unless the post is locked down, you have no way of knowing whether JB or his web mod will be seeing it and putting your name on a list of people to avoid. Which is not to say you shouldn't post that fantasy, just that putting it out there is not as anonymous an action as you might think, especially with some fans hellbent on outing others' fannish identities.
You are responsible for what you say. Say what you will, post that treatise on how skinny Actress C has gotten lately and why you think that makes her a terrible role model, tell people your honest opinion on the latest TV phenomenon, draw the caricature of that political figure. Just be aware that you're not posting in a vacuum, and that you may be held to that opinion by people who disagree, representatives from the company that owns the material you're shafting, and even the celebrity him or herself. If you can handle the fallout, go forth and post. If you think you're going to regret it in the morning ("I called who a WHAT?") then consider locking the post or sitting on it a few days. Or don't. The Internet is everyone's stage and we all take our share of the spotlight. You can use yours to blow off steam, or to complain about something that upsets you about your favorite comic, or to praise the acting choice Actress D made in that one scene in her last movie, or to talk about how you'd like to lick pudding off Actor E's pectoral muscles. Say what you need to. Post what you will. The consequences are yours for the accepting.