The first issue of the book of Samuel is with Samuel himself. What tribe was he from? Samuel was a Levite, something I never realized before reading this comment in the SAB. I'd always wondered how Samuel ended up where he did in life without being a Levite, but since he is one, no problem. Oh, how do I know? The verse here in 1Samuel never names the tribe of Ephraim, only the mountain of Ephraim. Levites lived all over the place, and Samuel's parents happened to live in Ephraim.
Now Samuel's father had two wives. The fact that the Bible mentions this without condemning it does not, in my mind, imply endorsement. In general, I stand on my previous statements on the matter, but recent political developments present me with an excellent example of the flaw in logic. I have recently written much on Proposition 8, the proposed amendment to the California Constitution banning same-sex marriage. In all my writing, I never endorsed either side of the issue. In failing to take a side, the logic here implies both (A) that I endorse same-sex marriage, and (B) that I endorse the banning of same-sex marriage. Clearly, I cannot endorse both and the fact is, I endorse neither. The Bible likewise by silence does not endorse any position on this matter.
As for the note on verse 5, I tend to think of a phrase like "the LORD had shut up her womb" as simply a colloquial way of saying "she had no children", which after all is what it boils down to. However, it may in fact be the case that God has made Hannah barren for the purpose of setting up the story we are about to see unfold. Samuel was one of the most important prophets in Israel's history, and without his mother's problems in procreating, his life might have been very different.
The story of Samuel's birth has some parallels to the stories of Samson and John the Baptist, and I call your attention to the former for my comments on long hair, which I think are implied to be applying in Samuel's case. The claim that Samuel's hair would never be cut implies that Hannah is dedicating him to the service of God.
The interchange between Hannah and Eli is an interesting one, because as a priest, Eli is supposed to be a representative of God*, and yet he keeps making largely baseless assumptions about Hannah without consulting God. First he assumes that she must be drunk because he sees her praying (huh?), and then in what I assume to be embarrassment, he more or less assures Hannah that God's going to grant her wish, without finding out what it was. This is why I tend to take it with a grain of salt when a person in the Bible says that such-and-such thing is the "will of God". Anyone, including Christians, can fall into the trap of setting too much store in such a statement. In this case, however, things turn out alright.
I honestly don't know what the SAB is on about with its last marginal note on this chapter. A married couple having sex is far from scandalous, so I guess the "sex" markup is just matter-of fact? The really interesting thing here in my mind (but I suppose it's not marked because it's not a contradiction or some such thing) is that after Samuel is born, Hannah tells Elkanah that she has dedicated Samuel with a vow. As mentioned elsewhere in the Bible, it's part of the Mosaic Law that a married woman's vow made without her husband's knowledge is not binding unless her husband allows it. Elkanah is really being quite kind to Hannah by ancient Israelite standards, allowing her vow to stand and essentially giving up his child. He would have been well within his rights in that culture to tell her she couldn't fulfill her vow, keep the kid and give him a haircut.
* There is an interesting and humorous facet to this story that's easy to miss. I know, because I missed it even this time reading it, despite already knowing about it. In the footnotes of Robert Alter's translation of Samuel, he points out that this is a typical "annunciation scene", also pointing out parallels between this story and those of the birth of Samson, Isaac, and John the Baptist. The weird bit is that when Hannah is sitting there praying for a son, it would be a typical time for an angel to appear and say, "Fear not, Hannah, for God hath heard thy prayer, etc..." Instead, a fat, half-blind, ineffective priest walks up to her and accuses her of being drunk. Eli has missed the fact that he's witnessing a moment of historical significance for the nation of Israel, and in doing so, he essentially flubs his lines.