Yes, MD5 is somewhat less CPU-intensive. On my Intel x86 (Core2 Quad Q6600, 2.4 GHz, using one core), I get this in 32-bit mode:
MD5 411
SHA-1 218
SHA-256 118
SHA-512 46
and this in 64-bit mode:
MD5 407
SHA-1 312
SHA-256 148
SHA-512 189
Figures are in megabytes per second, for a “long” message (this is what you get for messages longer than 8 kB). This is with sphlib, a library of hash function implementations in C (and Java). All implementations are from the same author (me) and were made with comparable efforts at optimizations; thus the speed differences can be considered as really intrinsic to the functions.
As a point of comparison, consider that a recent hard disk will run at about 100 MB/s, and anything over USB will top below 60 MB/s. Even though SHA-256 appears “slow” here, it is fast enough for most purposes.
Note that OpenSSL includes a 32-bit implementation of SHA-512 which is quite faster than my code (but not as fast as the 64-bit SHA-512), because the OpenSSL implementation is in assembly and uses SSE2 registers, something which cannot be done in plain C. SHA-512 is the only function among those four which benefits from a SSE2 implementation.
Edit: on this page (archive), one can find a report on the speed of many hash functions (click on the “Telechargez maintenant” link). The report is in French, but it is mostly full of tables and numbers, and numbers are international. The implemented hash functions do not include the SHA-3 candidates (except SHABAL) but I am working on it.