1. Exclamation points!!!!1!!!1!!1one1!!!
I saw this one on Slashdot first (someone needs to do a blog post on general Slashdot humor). The “!1one” actually has an entry in the Urban Dictionary, which explains it pretty well:

Used in long uses of exclamation marks, the !1one is an intentional mistake that jokes about the appearance of numeral value “1″ in exclamation overdoses. This is due to the shift key not consistantly being pressed while tapping “1″ for the overused “!”‘s. The intentional error may signify even more exclamation marks, like some kind of lunatic scientific notation. !1one may= !E9 or !*10^9, thus representing an absurd amount of exclamation.

2. Strike-through Jokes Joke Attempts
I imagine the practical origin of these jokes are real edits, where the author wanted to leave the original wording intact to denote the edit. However, a lot of strike-through “edits” are made before the first publishing with the intention of making a joke. Jokes like these are very similar to those in the “I’m not saying any names (Jason), but someone…” family. Here’s some strike-through action I did in an earlier post on this blog:

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3. Super-long Acronyms. ITLSDLATKOAYPTYA
Acronyms are great time savers in IM conversations. First there was ROTF, which stands for “rolling on the floor”. Then there was LMAO, which stands for “laughing my ass off”. And then some genius put them together to get, ROTFLMAO or “rolling on the floor laughing my ass off”. Acronyms as long as these encourage people to make up their own super-long acronyms. Mine above stands for “I’m talking like super-duper long acronymns. The kind of acronyms your parents told you about.” Next time you’re in an IM conversation with someone, try to throw a few of these super-longs in. It’s actually pretty amazing how well you can understand these, even when they’re made up on the fly.

4. Lots of links next to each other.
Another one I saw at Slashdot first. Excessive linking isn’t always meant as a joke, but there is often some humor with how the words connect to the material they are linking to. Chris Messina is one link-happy blogger who uses this technique a lot on his blog. Here are a few examples.