The xkcd forums are offline, and I don't know if they're ever going to come back online. You can still see the scores as of the most recent successful update, and graphs and looking at previous scores should still work. If the forums have come back online, it'll probably take me a couple days to get around to reenabling updates.
Some information about how exactly the scores are calculated:
Only what's visible in the thread to non-logged-in users counts. That means that seconds aren't taken into consideration (a post at 1:00:59 is the same as a post at 1:00:00), and that any forum clock changes or forum downtime isn't taken into consideration. Posts are (currently) counted in the order they appear, even if it's not the order they were posted in (can be different if two posts are made the same second).
Post content, including claims about how many points one has, are completely ignored (except in the "duck" threads).
Changes on earlier pages may confuse things.
The program (currently, if everything's working correctly) does not check the thread if it's checked in the last 10 minutes, and does not download more than five pages at a time. This is in case something goes wrong, like if a bot tries to load the page like 1000 times a second or something at least I won't overload xkcd's server... This is determined separately for each forum game.
Rule changes that retroactively apply to previous posts in a thread are generally easier for me than those that apply starting from the time they're changed, unless post content is involved. (The program stores a list of posts, and calculates the scores each time.)
The link in my signature will usually go directly to the current forum game, but doesn't always work if you're viewing a permalink to a post that hasn't been counted yet. (The URL of the page you're coming from is what matters; if there's a t=, then it's fine.) This page has a bookmarklet that you can use instead.
If you post twice in a row, the second post is completely ignored. E.g., if A posts at 1:00, A posts again at 1:15, B posts at 1:30, then B gets 30 minutes.
Thread Necromancy Slowmode
Double posts count towards your score. (This was never clarified to me, but that seems to be what people are doing.)
Posts that get 0 weeks can still block other players from getting time.
It only counts when the letters d, u, c, k appear consecutively in order, with nothing in between, as ordinary upper- or lowercase letters (but could be in the middle of a word)
HTML tags are ignored; this means link and image URL's don't count, but also means that something like d[s][/s]uck still counts as saying the word
Text in images or linked websites are ignored
Attachment filenames and file comments only count if they're placed inline (I may change this later)
If necessary, I can manually mark posts as containing or not containing the word.