These uint160/uint256 types internally use little-endian.

BinaryFormats.txt

@@ -36,6 +36,8 @@ Account IDs are based on the compressed public key. Apply SHA512 to the
 
 The resulting 20-byte value is the account ID.
 
+Keeping with the Bitcoin tradition, unsigned 160-bit and 256-bit integers
+(hashes, transaction IDs, account IDs) are sent in little-endian format.
 
 2) Transaction (source/signed format) 145-bytes
 

uint256.h

@@ -23,11 +23,11 @@ typedef unsigned long long  uint64;
 #define for  if (false) ; else for
 #endif
 
+// These classes all store their values internally
+// in little-endian form
 
 inline int Testuint256AdHoc(std::vector<std::string> vArg);
 
-// TODO: Do we need these things? Why not just use vector<unsigned char> ?
-
 // We have to keep a separate base class without constructors
 // so the compiler will let us use it in a union
 template<unsigned int BITS>