Some of the following are more along the lines of QYSA, but I hope that that doesn't matter overly.
Random comments from the first reading:
1.2: discussion, not disscussion
1.4: Might be worthwhile to give /emphasis/ to the word predates, since it seems a relatively common misconception that CL is an older dialect with obsolete cruft.
2.1: ECL is afaik the current name -- might be good to note that the sf project name "ecls" is both a historical artifact and due to ecl being taken on sf.
Poplog: is there anything happening there? If not, maybe it should not be listed.
SBCL: "SBCL runs on many Unix and Unix-like systems."
2.4: Probably woth mentioning common-lisp.net.
3: Add "undefined behaviour".
4.1: Just a pet peeve of mine: when showing what "Hello World" looks like there is little point in using format...
(write-line "Hello, World!")
4.5: Mention cl-ppcre.
4.8: Probably good to mention that doing the "local modification" to a function in the COMMON-LISP package is undefined behaviour.
5.1: Maybe something to the effect: "However, the problem here is actully not using a paren-aware editor. Interaction with the REPL is usually best accomplished from the comforts of an editor that integrates with the list. See XXX."
Cheers,
-- Nikodemus