A few time ago Twitter was pleases to announce they have applied to trademark "tweet" ,because they said it was clearly attached to Twitter from a brand perspective.
USPTO explained the rejection this way: "marks in prior-filed pending applications may present a bar to registration of applicant’s mark. [...] If the marks in the referenced applications register, applicant’s mark may be refused registration under Trademark Act Section 2(d) because of a likelihood of confusion between the two marks"
For Twitter is of course a bad news,but for us may be a good news,if you think that many people have the word "tweet" in their domain names.