I love 521s for their indestructability (well, almost indestructable.  I only broke 4:p) 
 
evry1 sed/sez DX32isms r cheese rims or really really heavy.  well, yeah.  they is noticably heavier till built up into a wheel and shoved on ur bike.  remeber, a 521 wheel with mich comp tyre will b heavier than a DX32 wheel with light tyre.  but hey.... 
 
I (reluctantly) went for an Onza Full Fat and...errrrr...YAY!!!!!!!!!   when I  started doin spinny street tricks, my tyre was folding loads on a 521 and causing me many spills.  I haven't had a tyre fold since using a wider rim.  and I don't notice the extra weight, even since goi to a nice heavy comp 16!!! 
 
get one.  yes 521s r brilliant, but DX32isms r just as good!  tried and tested: FACT!!!!! 
 
smithy