Tested in Windows XP Professional
Drive y: is mapped to my solaris home /home/rg157576 through samba, and permissions for the file is
bash-3.00$ pwd
/home/rg157576
bash-3.00$ ls -al testfile
----------   1 rg157576 staff          0 Dec 29 11:22 testfile

The file testfile doesnt have any permissions, still File.canExecute(),File.canRead() results true.
See the following version,code and result.

<Version>
C:\work>java -version
java version "1.6.0-auto"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.6.0-auto-346)
Java HotSpot(TM) Client VM (build 1.6.0-rc-b64, mixed mode)
</Version>

<CODE>
import java.io.File;
class TestCanEx {
    public static void main(String ... s){
       File f = null;
       try {
         f = new File(s[0]);
         boolean b = false;
         b = f.exists();
         System.out.println("is exists" + b);
         if (b) {
            System.out.println("Can Read    " + f.canRead()); //Returns true, not correct
            System.out.println("Can Write   " + f.canWrite()); //Returns false, correct
            System.out.println("Can Execute " + f.canExecute());//Returns true, not correct
		 }
       } catch(Exception e){
          System.out.println(e);
       }
     }
}
</CODE>

<Result>
Result when execute:
C:\work>java TestCanEx y:/testfile
is existstrue
Can Read    true
Can Write   false
Can Execute true
</Result>
Spec for File.set{Readable,Executable}() says:
   'Returns true if and only if the operation succeeded.'

I have a file 'testfile' on the drive y: of Windows Xp Prof. mapped to solaris home through samba and permission for the file is
bash-3.00$ ls -al testfile
----------   1 rg157576 staff          0 Dec 29 11:22 testfile

File.set{Readable,Executable}() returns true, but does not change the permissions.
As mentioned in the spec it should return false.
Please see the following code and Result
<Code>
import java.io.File;
class TestExecute {
    public static void main(String ... s){
       File f = null;
       try {
          f = new File(s[0]);
          boolean exists = f.exists();
          System.out.println("is exists: " + exists );
          if (exists) {
  	         boolean bool =false;
	         for (int i=0;i++ < 2;) {

                System.out.println("f.setReadable(true,"+bool+")   :"+f.setReadable(true,bool));
                System.out.println("f.setReadOnly()             :"+ f.setReadOnly());
                System.out.println("f.setWritable(true,"+bool+")   :" +f.setWritable(true,bool));
                System.out.println("f.setExecutable(true,"+bool+") :"+f.setExecutable(true,bool));
                System.out.println();
                bool = !bool;
             }
	       }
       }catch(Exception e){
         System.out.println(e);
         }
     }
}
</Code>

<Result>
C:\work>java TestExecute y:/testfile
is exists: true
f.setReadable(true,false)   :true
f.setReadOnly()             :false
f.setWritable(true,false)   :false
f.setExecutable(true,false) :true

f.setReadable(true,true)   :true
f.setReadOnly()            :false
f.setWritable(true,true)   :false
f.setExecutable(true,true) :true

Permissions of the file after executing the program :
bash-3.00$ ls -al testfile
----------   1 rg157576 staff          0 Dec 29 11:22 testfile
</Result>

 when compared with File.setReadOnly(), File.setWritable() returns false as the access is denied in Windows platform.