I wrote a little script that went trough a few curl tarballs I have lying
around (I don't have many of the very old ones). I had 'wc' report on all
files ending with .c or .h and thus, the curl source growth is as follows:

Archive Lines Words Bytes Approx date
curl-4.8.tar.gz 3803 14673 113412 Sep 1998
curl-5.9.tar.gz 13220 48780 377622 May 1999
curl-6.0.tar.gz 15064 55411 427146 Sep 1999
curl-6.1.tar.gz 15645 57534 444777 Oct 1999
curl-6.2.tar.gz 15626 57503 444368
curl-6.3.1.tar.gz 15951 59077 456775 Nov 1999
curl-6.4.tar.gz 16427 60947 469289 Jan 2000
curl-6.5.2.tar.gz 17388 64253 502096 Mar 2000
curl-7.1.1.tar.gz 19508 72164 566606 Aug 2000
curl-7.2.tar.gz 19666 72664 570845
curl-7.2.1.tar.gz 19679 72736 571456
curl-7.3.tar.gz 21518 78666 620971 Sep 2000
curl-7.4.1.tar.gz 22237 81237 642429 Oct 2000
curl-7.4.2.tar.gz 22539 82253 651960 Nov 2000
curl-7.5.tar.gz 22753 82847 657902 Dec 2000
curl-7.5.1.tar.gz 22807 82992 659309 Dec 2000
curl-7.5.2.tar.gz 21988 81368 642112 Jan 2001
curl-7.6.tar.gz 22243 82676 655685
curl-7.6.1.tar.gz 22736 84358 669485 Feb 2001
curl-7.7.tar.gz 24408 90865 722701 Mar 2001
curl-7.7.1.tar.gz 24499 91326 727184 Apr 2001
curl-7.7.2.tar.gz 24636 91873 731616
curl-7.7.3.tar.gz 25317 94109 750521 May 2001

-- 
  Daniel Stenberg -- curl project maintainer -- http://curl.haxx.se/