Why, oh why do I always click, "Post Anonymously"? Seems I get far more +5s as an AC than as meself. The mods stop at +3 when I'm posting under me own name!
Interesting fact: It depends on where you look at your posting and whether or not you have "Excellent" Karma.
There are two ways to look at your posting: From the article's comment section and from your own comment history on your profile.
If you're an AC, your comment gets a nifty 0 moderation. People need to upmod you 5 times until it's at +5.
If you're logged in, you get an immediate +1 that is visible to you and everyone. People only need to upmod you 4 times until it's a +5.
If you have "Excellent" Karma, you get another +1 putting your posting at +2.
Since people stop moderating when a comment reaches +5, your own history will never show them as more than +4.
If then someone downmods it only once shortly before the thread is archived (and moderation gets closed), your posting will sit at +3 in your history forever
You see, you don't even need Slashdot Beta for the posting system not to make any sense.