I checked each post on your main page that had a "read more" both while logged in and logged out in Safari, Opera, Firefox 10 and I even started up Chrome (which I despise). There was one post that didn't go exactly to the read more location and ended up at about 1/2 way through the image prior to the read more. Other than that, everything worked as it was expected.
** Safari logged in or logged out, no difference (except for the 28px difference due to the admin bar.
** Opera logged in or logged out, no difference (except for the 28px difference due to the admin bar.
** Firefox 10 logged in or logged out, no difference (except for the 28px difference due to the admin bar.
** Chrome logged in or logged out, no difference (except for the 28px difference due to the admin bar.