I'll occasionally ride in street clothes, but much prefer to wear cycling-specific gear (or at least technical gear...my array of fluorescent $10 shirts from target see heavy rotation in spring/fall).

The sweat doesn't have to be an issue 8-9 mo out of the year (summer= sticky/humid/gross), but I do use my commute (11 mi/one way) as cardio, so I like to move at a good clip.

For me, the bigger issue is that commuting in work clothes (usually jeans) is really, really uncomfortable over 20+ miles/day and also my jeans get worn out much, much faster when I ride in them all the time (inner thigh + saddle nose = holes....). So, in the long run, it saves $$$ to just wear bike gear on the bike and work gear at work