Like writing messages on the ground in Nethack?

The problem is they keep advertising this as an MMO when it's not. It's an Online RPG pure and simple.

I am also against this decision, you are there to kill things not to chat.

I am worried none of you got the Demon's Souls reference (Which uses a cross-instance message system just like this). This saddens me.

Demon's Souls is a PS3 action-RPG that is generally considered single-player (but there are co-op and PvP modes integrated into the single player game). When played online (single player online) you may leave notes on the ground (Which appear as brightly glowing generic runes until you touch them) that can be viewed by other players in other instances. These may warn of traps, hint at enemy weaknesses, or simply provide flavor (the most commonly referenced of which is the line "The true Demon's Souls starts here!"). Demon's Souls, however, does not have any randomized levels which means that most of the hint messages are immediately relevant to the level you are playing.

These messages are chosen from a pool of pre-made messages that sometimes have ad-libs style blanks you can fill with one of a hundred nouns or verbs from a list. Spiral Knights may get away with allowing players to have a 20-144 character message of their choosing.

There is also a system for allowing players to recommend messages that are good, which rewards the player who wrote the message with a small boost of health. The health boost would be out of place in Spiral Knights and I would not recommend it, but the recommendation system could be sound for culling low-quality ramblings.

Also, it seems the Demon's Souls wiki is currently running advertisements for Spiral Knights. Weird coincidence!

I remeber someone talking about a preview event level where there was a Knight's "diary" (logbook) detailing aobout how he fed the slimes, making them non-hostile.

Of course, that was built into the level and wasn't player made, but if along with dungeon chat, we had such logbooks laying around? Their appearance would be a blue cube projecting a hologram. If you press attack next to it, an interface appears.

Here you can read what messages Knight's have left, whether detailing of their adventures, warning about future traps, finding which weapons are best against teleporting wolvers, what loot they collected, etc.

Alternatively, you could write your own and help (or just leave messages to) other knights.

The logbooks appear about mid-way through each depth and are sorted by date. When a new gate is created or a week goes by, the logbooks are wiped clean.