(These are sorted by how irritating they are.  The worst bugs are at the top.)

- It is impossible to edit or view the same file more than once.  It is
  also impossible to invoke Elvis twice with no arguments when in the same
  directory.  This is caused by the way the temp file is named based on ".",
  see function tmpstart() in tmp.c.

- Inserting characters to make a line longer than BLKSIZE-1 (including the
  newline) causes a crash.  BLKSIZE is 1024 by default.  The shift-J and :join
  commands protect against this, but something like "9999a!<Esc>" will make
  Elvis misbehave.  Also, huge files (more than about 500k) cannot be edited.

- autoindent is confusingly different from vi when editing typical
  indented C code - e.g. after <ESC>o<ESC>xxxxxxxxxxi (x's to column 1)
  the last i indents again.

  ^U backspaces to the beginning of the line, but it should only backspace to
  the start of auto-indent.  (A second ^U could reasonably delete the indent
  too)

- The :@ and :source commands share a single buffer.  This means that they
  can't call each other.  You can't run :source from within your .exrc file
  either, for the same reason.

- Commands which delete text before the cursor, such as `dB', don't move the
  cursor, but they should.  

- Using the substitute command, it is not possible to replace with multi-
  line text using the ^V^M construct in the replacement string.  Vi allows
  this as a special case.

- The Elvis.prj file (used by Turbo-C under MS-DOS) does not force large model
  and the text segment is > 64K.

- The visual "put" commands can't be repeated by hitting ".".

- "!!ls %" doesn't expand %

- Sideways scrolling is unacceptable for slow terminals.

- The ":set number" option is missing, among other things.

- In DOS, the default colors are not very good.