Just in case I'm not the only person still using one of the 7.0.x versions of IntelliJ IDEA, be aware that if you run it with JDK 1.6 its Subversion features will not work. For example, if you pick "Browse Subversion Repository..." from the "Version Control" menu nothing will happen; you won't even get an error message. The good news is that the nice folks at JetBrains have a fix for this problem, in the form of a new version of the built-in Subversion plug-in. As a Mac user who upgraded to Mac OS X 10.6, AKA "Snow Leopard", Java 1.6 is all I can run, so this was a vital fix for me.
My thanks to Serge Baranov for his prompt and helpful response to this problem.
(And, for anyone, like me, who managed to miss it, there is an IDEA 7.0.5 release.)
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P.S. Serge notes that this issue won't affect most Windows users, because IDEA 7 was bundled with an older version of Java 1.6 in which this problem does not manifest. However, users of Mac OS X 10.6 (and 10.6.1) are using Java version 1.6.0_15 (there's no choice), in which the problem does manifest. Linux users will also encounter this problem if they use Java version 1.6.0_12, or later.