Missing article added.
Consistent (at least in this file) use of abbreviation.

Enumeration lists with bipartite entries could be harder to read than
two-column tables.

Assignment and equality are not the same.

Moreover, there seems to be a bug in Rails 2.3.0: After editing the view file
apps/views/greetings/hello.html.erb in Vim, WEBrick ships the outdated content
from the backup file apps/views/greetings/hello.html.erb~ instead of the
intended content. Only when the 'tilde backup' file is not present, the browser
shows the correct contents (both Konqueror and Firefox; you can even add a
_different_ hello.html.erb~ to show completely different stuff).

This bug does not occur in Rails 2.2.2.

Add active links to internal sections.
Use textile markup for particular words.
Improve the indentation in code examples.
Fix some typos.

for <code> elements
for (monospaced) displayed material
add some commas in enumerations.

Change the wording at several places to improve the reading flow.
Sprinkle some commas into the text.

A second occurrence of unmatched 'code' markers.
Plain HTML tags are not rendered at all, so use named HTML elements instead.