While changing MACs on your NIC is perfectly acceptable, one thing that will get you noticed is repeatedly changing MACs and getting new IPs - luckily, since this involves a lot of hassle, no one's likely to do it accidentally, but someone leasing several hundred IPs (because your old one is still leased) will get spotted, cut off and talked to remarkably quickly.
And yes, we should listen to people who are being DDosed, although I'm not totally sure what we can do (report the DOSer I suppose, but gathering the evidence is hard).
And whoever said turn your modem off for four hours to get a new IP should get a clue - the lease time is at least 48 hours these days.