Relatively small set of lines with differences in most lines can destroy
the performance of difflib.HtmlDiff.make_table and difflib.ndiff.
I am using it like this:
    ...
    htmldiffer = HtmlDiff()
    return htmldiffer.make_table(src_lines, dst_lines, 
        fromdesc="file1",
        todesc="file2",
        context=True)

I have written the src_lines and dst_lins to files and tried this with
the Tools/scripts/diff.py wrapper with same results when using the
switches -m or -n.
The performance is fine when using difflib.unified_diff or switch -u on
diff.py

Attached are files that show this clearly.
left200.txt,right200.txt - 200 lines of text - duration 11 seconds.
left500.txt,right500.txt - 500 lines of text - duration 2min 58 sec
left1000.txt,right1000.txt - 1000 lines of text - duration 29min 4sec

tested on Intel dualcore T2500 2GHz with 2 GB of memory, python 2.5.2 on
Ubuntu. Same problom on python 2.6 on Fedora-11
For reference, the kdiff3 utility performs beautifully on these files.