I understand microevolutionary change to be small changes for example the timing of events such as flowering in plants or emergence in insects. For example in monkey flowers the gene that allows one population of the plant to survive on copper contaminated soils directly prevents reproduction with other monkey flowers that do not live on copper contaminated flowers. Natural selection for copper tolerance led directly to reproductive isolation.
I agree the study of speciation has been a bit of a mess but this is beginning to change, this article is a good intoduction to the recent changes in the study and unserstanding of speciation:
http://abacus.gene.ucl.ac.uk/jim/pap/malletjeb01.pdf
There is alot of research that has gathered good epirical evidence and it is listed in the reviews i mentioned, here are some more primary refernces if people are interested:
A. P. Hendry. Adaptive divergence and the evolution of reproductive isolation in the wild: an empirical demonstration using introduced sockeye salmon. Genetica 112—113: 515—534, 2001.
Schemske, D.W. and Bradshaw, H.D., Jr (1999) Pollinator preference and the evolution of floral traits in monkey flowers (Mimulus). Proc. Natl. Acad. Sci. U. S. A. 96, 11910—11915 Nagel, L. and Schluter, D. (1998).
Nagel, L. and Schluter, D. (1998) Body size, natural selection, and speciation in sticklebacks. Evolution 52, 209—218.
Via, S. et al. (2000) Reproductive isolation between divergent races of pea aphids on two hosts: selection against migrants and hybrids in
the parental environments. Evolution 54, 1626—1637.