Current situation:

Type of data: User-entered texts all over Moodle, after filters have been applied and converted to HTML
Data structure: One simple HTML text, keyed by MD5 of original text concatenated a variety of params like context, filter settings, language etc
When it gets stored: At the first time the text is displayed
Where it gets stored: In table cache_text
How it gets read: Next time the text is displayed, if within the $CFG->cachetext timeout period
Does it need locking: No
How it gets cleared: Cron job cleans anything older than $CFG->cachetext
Typical sizes: 1k
Safeguards in place (eg limits): None

Bonus caching within this caching:

A static variable $croncache[$md5key] = $text; is being used during CLI operations only (eg cron) to store the last 150 texts. MDL-13310