use is one of those words which historically has been used to mean a whole lot of different things -- OED2 lists 25.. no, 26 senses. only a few of these are intransitive, e.g.:

20. To do a thing customarily; to be in the habit of so acting or doing; to be wont to do. (Chiefly in clauses introduced by as, and now only literary.)
[first attested in 1380] 1875 BROWNING Aristoph. Apol. 365 Die at good old age as grand men use.

which leads to:
21. With to and inf.: To be accustomed or wont to do something.
In very frequent use from c 1400, but now only in pa. tense used to, with pronunc. (just tu, just), and colloq. in did (not) use (or used) to: see also USEN'T, USETER; used to could.
[attested to Chaucer in 1385] 1670 MILTON Hist. Eng. VI. 304 The English then useing to let grow on their upper-lip large Mustachio's. 1728 GAY Begg. Op. II. iv, You are not so fond of me, Jenny, as you use [sic] to be. 1767 Woman of Fashion II. 26 How did we all use to admire her! 1837 LOCKHART Scott I. iv. 122 He used to get all the copies of these ballads he could. 1873 C. M. YONGE Pillars of House II. xvi. 105 Did Alda use to be nice, or is it love? 1884 W. C. SMITH Kildrostan 53 You used to be a leal, true-hearted girl. 1925 S. LEWIS Arrowsmith xviii. 192 Didn't we used to have fun. 1927 E. HEMINGWAY Men without Women 154 He certainly did used to make the fellows he fought hate boxing. 1935 E. FARJEON Nursery in Nineties III. i. 124 Mama, did you use to be a flirt? 1963 V. NABOKOV Gift ii. 117 And now I continually ask myself what did he use to think about in the solitary night. 1974 Radio Times 28 Feb. 25, I suppose I did use to be a prophet of doom.

of course, the OED being historically descriptive, this all says nothing about the "correctness" of using "used to" vs. "use to"..