I got pretty comfortable wearing a speedo considering I swam and played water polo through HS and college. If you are in shape, girls find it pretty hot.
BTW, there are 2-3 major styles of men speedos. One's that look like the pics linked (like briefs), and then those that look like the ones Daniel Craig wore (more like boxer briefs). The 'briefs' style is further subdivided between the euro and american style which differ on how high they sit on your leg and how low they go on the waist.