One big problem with SERi has been the complexity of the SER configuration language. Only apache (httpd) can (almost) compare in the flexibility and number of ways a piece of software can be configured. This has resulted in a pretty steep learning curve for beginners. SIP can be used for an increasing number of applications and each deployment has its own, specific needs. Thus, SER's configuration language must be powerful.
The professional SER user has other issues, like maintaining multiple configurations across server farms and setups, sharing some code, but still needing individual tailoring to each server. '