Real time scanning and file extension exclusions
(Please note that I advocate no exclusions at all for off-line scanning such as manual or scheduled scans. In these cases performance is not as much of an issue as with realtime scanning.)
As of today, files with a .log extension are not executable under Windows and I don't see that changing very soon. As such .log files pose no direct threat to the security of any windows computer.
An interesting experiment would be to create a windows shortcut to an executable file and call it 'tst.log'. See if you can manage to execute the original executable file by means of 'tst.log' alone.
If these files were to be used as payload containers for illicit code, they would still need a loader/executer/interpreter to be effective. This loader/executer/interpreter would necessarily be contained in a executable file which can and will be inspected by ao anti-virus software.
Hence there is no actual benefit for the malware writer to use .log files as payload containers unless he would endeavour to create a loader/executer/interpreter that would be too generic to be detected by explicit virus definitions and not generic enough to be detected by heuristic rules. I consider it highly unlikely that such software could succesfully be made and escape detection from all realtime scanners.
Therefore I would indeed recommend to exclude any .log files from realtime scanning. In fact I would advocate to add exclusions for many more extensions: .txt, .cpp, .obj, .bmp and *.cfg to name but a few.
The main benefit is of course reclaiming the lost performance due to realtime scanning of files for which realtime scanning offers no security benefits.