CPLR R. 3116 Signing deposition; physical preparation; copies
(a) Signing. The deposition shall be submitted to the witness for examination and shall be read to or by him or her, and any changes in form or substance which the witness desires to make shall be entered at the end of the deposition with a statement of the reasons given by the witness for making them. The deposition shall then be signed by the witness before any officer authorized to administer an oath. If the witness fails to sign and return the deposition within sixty days, it may be used as fully as though signed. No changes to the transcript may be made by the witness more than sixty days after submission to the witness for examination.
David Horowitz has a great article in New York State Bar Association Journal about the use of unsigned deposition transcripts in summary judgment motions titled "Signature Required." As we all know, summary judgment must be supported by proof in admissible form. And generally, unsigned deposition transcripts are not proof in admissible form. Why? CPLR R. 3116(a), requires that the deposition transcript be signed by the witness. If that isn't done, the transcript may be admissible provided that the transcript was actually provided to the witness for his or her signature within 60 days of receipt. The rule is not without it's exceptions, however. For example, "When a party moving for summary judgment utilizes an unexectuted transcript of its party witness, thereby 'adopting' the contents...and the transcript is then relied on by the party opposing the motion, the transcript may be considered as proof in opposition by the opposing party." (quote is from the article. I have no idea how to cite to it). Another example is when it is used as a party admission. You'll have to read the article to get all the cites. If not for the cites, you should read it, just because.
Oh, ok, just one cite, Pina v. Flik Intern. Corp., 808 N.Y.S.2d 752 (App. Div., 2nd, 2007). There the Appellate DIvision makes it pretty simple. Either it's signed, or you show that you sent it to be signed. Otherwise, you're screwed:
The Supreme Court properly denied the defendants' motions for summary judgment since they failed to submit sufficient evidence in admissible form to establish their entitlement to judgment as a matter of law (see Winegrad v New York Univ. Med. Ctr., 64 NY2d 851, 853 ). The defendants failed to show that the unsigned deposition transcripts of various witnesses they submitted in support of their motions had previously been forwarded to the relevant witnesses for their review pursuant to CPLR 3116 (a). Hence, contrary to the defendants' contention, they were not admissible (see Lalli v Abe, 234 AD2d 346 ; Palumbo v Innovative Communications Concepts, 175 Misc 2d 156 , affd 234 AD2d 346 ; Connors, Practice Commentaries, McKinney's Cons Laws of NY, Book 7B, CPLR C3116:1).
Yes, I know, there are exceptions, but generally, you will be screwed.
Compare Pina with St. Vincent’s Hosp. & Med. Ctr. v Allstate Ins. Co., 2010 NY Slip Op 00668 (App. Div., 2nd, 2010). In that case the defendant offered several unsigned EUO transcripts as evidence in support of its motion for summary judgment. Defendant offered them under the theory that (1) they weren't being offered for their truth and (2) they were admissions. The Appellate Division found that defendant's cross motion should be have granted, reversing the lower court. The Appellate Term, twice now, has held that assignors are not parties. I read defendant's briefs, but don't quite understand just how defendant thought the transcripts were relevant if not offered for their truth. JT appears equally confused. And the Appellate Division's decision offers zero insight. The whole thing is weird.
So, in conclusion, make sure to read the article. It was the first thing I turned to when I opened the magazine. I'm a nerd. Fat too. God help me.
 Sorry, I forgot to add something. In the very beginning of the article Mr. Horowitz briefly discusses the history of summary judgment, including the initial fight as to whether, and I'm paraphrasing here, it encroached on the right to trial by jury. The issue of whether summary judgment is constitutional, it appears, is not a new argument. If anyone is interested, there is a great Law Review article on that very topic. I posted it back in September with links to the articles.