This page maintains obscure screenshots. Spoiler and nudity warning for some links. Serious spoilers! Better not read this page until you watched the whole series...
Censored bit from #2: Animax's version shows less of Midori's body, and puts on their usual watermark.
New opening in #7: As of episode #7, Midori now wears clothes in the flower falling scene, and the background circles are now more colorful.
Old opening in #8: TV Kanagawa's broadcast on 2004-05-23 reverted back to the old opening, but the later broadcasts on the next day (Chiba TV and TV Saitama) used the new opening.
Last episode opening / final ending: the first 20 seconds look very similar, except the flowers are different:
The rest of the opening is completely different, except Midori still sits on Seiji's right hand side.
Changing seasons: three sets of tree colors for the title screen (1-6, 7-10, 11-13). Last part of the last episode completes the seasons.
Ultra Marin: Takamizawa's Ultra Marin.
Aikawa Shou: Seiji's poster + coffee collection.
Gugulu: it's not "Google" that Takamizawa was using in #9, but looks very similar.
By the way, screenshot above shows Gugulu returning 876000 results, actual number of results returned by Google as of 2004-06-02 is 728000.
See what 2ch people are saying about fansubbers: