On hardware, I installed AsteriskNOW1.5 and before doing anything other then the bug fixes, I downloaded the upgrade module and ran it. When I went to do the framework upgrade (by itself) I got:

Upgrading to 2.8.0alpha1..OK
Upgrading to 2.8.0alpha2..
-> Running PHP script /var/www/html/admin/modules/framework/upgrades//2.8.0alpha2/tables.php
Create dahdi table..ok
Checking if trunk_dialpatterns table exists..created
migrating rules..[FATAL] SELECT * FROM trunks_dialpatterns [nativecode=1146 ** Table 'asterisk.trunks_dialpatterns' doesn't exist]SQL - 
SELECT * FROM trunks_dialpatterns

and now if I try to go back to /admin/config.php I got:

FATAL ERROR

SELECT username, password_sha1, extension_low, extension_high, deptname, sections FROM ampusers WHERE username = 'admin'
DB Error: no such field

Trace Back

Array
(
    [0] => Array
        (
            [file] => /var/www/html/admin/functions.inc.php
            [line] => 1313
            [function] => die_freepbx
            [args] => Array
                (
                    [0] => SELECT username, password_sha1, extension_low, extension_high, deptname, sections FROM ampusers WHERE username = 'admin'

DB Error: no such field
                )

        )

    [1] => Array
        (
            [file] => /var/www/html/admin/functions.inc.php
            [line] => 412
            [function] => getAmpUser
            [args] => Array
                (
                    [0] => admin
                )

        )

    [2] => Array
        (
            [file] => /var/www/html/admin/header_auth.php
            [line] => 23
            [function] => ampuser
            [class] => ampuser
            [object] => ampuser Object
                (
                    [username] => admin
                    [_password] => 
                    [_extension_high] => 
                    [_extension_low] => 
                    [_deptname] => 
                    [_sections] => 
                )

            [type] => ->
            [args] => Array
                (
                    [0] => admin
                )

        )

    [3] => Array
        (
            [file] => /var/www/html/admin/header.php
            [line] => 157
            [args] => Array
                (
                    [0] => /var/www/html/admin/header_auth.php
                )

            [function] => include
        )

    [4] => Array
        (
            [file] => /var/www/html/admin/config.php
            [line] => 54
            [args] => Array
                (
                    [0] => /var/www/html/admin/header.php
                )

            [function] => include
        )

)

I suspect it would have gone better if I had brought FreePBX up to 2.7.x before trying to leap from 2.5 to 2.8. Which I am going to try next on another fresh install.