You should also consider that many link lists will not list you if you use free sponsor content. That stuff tends to get overexposed real quick.
About using mouseovers to hide affiliate codes. Its simply to make the link more appetizing... not because someone might change your codes. Surfers will be more interested in clicking on a link that in the status bar reads as "http://www.somesite.com/" instead og "http://www.somesite.com/tacking.cgi?userid=yaddayadda?someotherparamter=moreyaddayadda"... if you know what I mean
