Google Postini Service can never compete in terms of look-and-feel. Or rather, Google has never been bothered too much with slick design. They place their focus on functionalities instead.
For example, in IMHS, there is no way for administrator to know how many accounts he has created so far. I can understand that it's convenient for a CSV upload utility. It's helpful and most welcomed. However, after importing, there must be an intuitive way to show the list of imported users.
Google Postini Service's experience, again, is vastly different. A list of user accounts is shown distinctly. What's more? There is a way to adjust anti-spam for different categories (Sexually Explicit, Get Rich Quick, Special Offers, Racially Insensitive) at per-user level.
For each category filter, there is a way to set a base level (from Lenient to Aggressive).