I just pulled Steve McConnell's (must read!) CODE COMPELTE: A Practical Handbook of Software Construction off my bookshelf. The section How Long Can a Rountine Be? references some surprising (but perhaps dated) studies that suggest the evidence in favor of short routines is "very thin" and the evidence in favor of longer routines is "compelling". These studies are probably biased to desktop and corporate software written in C during the 1980s.

The consensus is that routines should have fewer than 200 LOC, but that routines shorter than ~30 LOC are not correlated with lower cost, fault rate, or programmer comprehension. btw, the longest function I've seen in commercial software I've worked on was 12,000 LOC! I will not name names. :)

* A study by Basili and Perricone found that routine size was inversely correlated with errors; as the size of routines increased (up to 200 LOC), the number of errors per LOC decreased (1984).

* Another study found that routine size was not correlated with errors, even though structural complexity and amount of data were correlated with errors (Shen et al. 1985)

* A 1986 study found that small routines (32 LOC or fewer) were not correlated with lower cost or fault rate (Card, Church, and Agresti 1986; Card and Glass 1990). The evidence suggested that larger routines (65 LOC or more) were cheaper to develop per LOC.

* An empirical study of 450 routines found that small routines (those with fewer than 143 source statements, including comments) had 23% more errors per LOC than larger routines (Selby and Basili 1991).

* A study of upper-level computer-science students found that students' comprehension of a program that was super-modularized into routines about 10 lines long was no better than their comprehension of a program that had no routines at all (Conte, Dunsmore, and Shen 1986). When the program was broken into routines of moderate length (about 25 lines), however, students scored 65% better on a test of comprehension.

* A recent [sic!] study found that code needed to be changed least when routines averaged 100 to 150 LOC (Lind and Vairavan 1989).

* In a study of the code for IBM's OS/360 operating system and other systems, the most error-prone routines were those that were larger than 500 LOC. Beyond 500 lines, the error rate tended to be proportional to the size of the routine (Jones 1986a).

* An empirical study of a 148 KLOC program found that routines with fewer than 143 source statements were 2.4 times less expensive to fix than larger routines (Selby and Basili 1991).