What was this poem about?

Emily Dickinson's poem "I'm Nobody! Who are you?" is about the individual vs. society and the theme of notoriety vs. anonymity. 
This short poem is only two stanzas long. The first stanza reads:

I’m Nobody! Who are you?
Are you – Nobody – too?
Then there’s a pair of us!
Don’t tell! they’d advertise – you know! (1-4)

This first stanza establishes the anonymity of the speaker; she is "Nobody." She has no name or reputation. The implication is that she is "Nobody" in the eyes of the society around her. However, she tries to establish a connection with a second person, whom she asks, "Are you -- Nobody -- too?" (2). The speaker seems excited by the possibility that she has met another Nobody, as she exclaims, "Then there's a pair of us!" (3). She speaks to this other person in a conspiratorial tone, exhorting him or her "Don't tell!" (4). Then the speaker establishes an "us vs. them" conflict when she says "they" would "advertise." The "they" referred to in line 4 seems to be society at large, from which the speaker and her new friend are isolated. The speaker ends the stanza with another conspiratorial remark: "you know!" This reiterates the commonality between the speaker and the other person; it is these two against the world.
The second and final stanza continues:

How dreary – to be – Somebody!
How public – like a Frog – 
To tell one’s name – the livelong June – 
To an admiring Bog! (5-8)

Here, the speaker elaborates on her own attitude toward notoriety vs. anonymity. She says it would be "dreary -- to be -- Somebody!" (5). The speaker then goes on to use an extended simile to compare being "Somebody" to "a Frog" that constantly says its own name "To an admiring Bog!" (6, 8). The speaker implies that being "public" (6) is not desirable. The image of the frog and its bog are not flattering; the simile suggests that those who live in the eyes of society and rely on society for approval are loud and ugly. This final thought reiterates the us vs. them conflict established in the first stanza and furthers the speaker's central idea that it is preferable to be "Nobody."