Long Answer:
128kbps is usually the standard meaning "Near CD Quality" i.e. virtually impossible for the untrained, inexperienced ear to tell even the slightest difference.
Encoding higher takes longer and uses up more disk space for a difference that few people will notice.
What I hate is fuckers who encode at 64-96kbps because they are lazy and have small hard drives. Damn them to hell.
-Warik