I used ClearCase for ten years or more, even worked at Rational for a while. I'm very aware of the power of the advanced features, and I'm not at all claiming that Subversion is point-for-point equivalent.
But at the same time, I'm also aware of a lot of limitations of ClearCase. It's very expensive in terms of compute resources and administrative support, for example. Some of the coolest features end up not being used at all, in many shops, because of platform compatibility issues (compatibility, incompatibility, and inter-compatibility), or problems when people take their laptops out of the network, or evolutions in language-processor design that violate the config-rec model. High-power items like config specs can be a lot of rope, and we've all hung ourselves more than once. Delightfully visual representations like the version tree can knacker the server(s) in no time.
The Subversion community began with a notion of how to do branches and tags really cheaply. In as much as I once worked in a large, globally distributed ClearCase shop where we had two engineers fully employed, 24x7, just making release tags, "cheap tags" gets my attention! With Subversion's cheap tags, you can safely tag what goes *into* a build, and let the build and test cycles tell you whether it's any good. And if it's not, you can safely remove the branch or tag, or file it away in some subdirectory where it needn't distract people--whatever fits your process--and none of these tag creations and adjustments need take longer than five seconds. Ever.
An additional advantage that should interest this audience is that the "global revision number" (which is the heart of the cheap-tag secret) is also a "global change number," suitable for tracking purposes in a sophisticated CM system. The appropriate Subversion commands can take either a "--revision REVISION" flag (which means "the that-version of everything") or a "--change REVISION" (which means "just the changes that went into that one commit"). In this way, the revision/change number can be tracked, reviewed, applied to related branches, and all the other change-centric stuff that can make a real difference for the CM process.
It's certainly true that ClearCase, as the latest product of over 30 years' evolution, has a head start over Subversion in some areas. CollabNet has attempted to help out, by supplementing the community's core contributions, with such add-ons as branch-and-merge wizards, change-based tracking tools, and the like, but there are still some holes and rough spots. But some of the simplicities are intended: just because you want something, such as change-tracking, does not necessarily mean you want to spend an arm and a leg to get it. A little rethinking about how you really want to use changes, a novel tool like cheap tags, and you may have a better solution than you did before. Different, yes. But better.