I see in the sourcecode this two lines:

// Do this infrequently and randomly to avoid giving away
// that these are our transactions.

in the method ResendWalletTransactions. Why is this necessary? If a client send out his transactions every 30 minutes and the receiver put these transactions in his own queue and send this transaction list every 30 minutes to all his neigbors I don't see why someone should recover the own transactions of the client.

The full beginning of the method is something like:

void CWallet::ResendWalletTransactions()
{
    // Do this infrequently and randomly to avoid giving away
    // that these are our transactions.
    static int64 nNextTime;
    if (GetTime() < nNextTime)
        return;
    bool fFirst = (nNextTime == 0);
    nNextTime = GetTime() + GetRand(30 * 60);
    if (fFirst)
        return;