I use to ride the 1.5 miles into work in my work clothes...until I started wearing through the thighs of my pants (Big & Tall store size pants can get expensive to replace every couple months).
I also got tired of being semi damp all day at work (this IS Texas).

So now I ride with the bike shorts under regular shorts or sweats (trying not tho scare the children) and change into nice dry clothes at work. Changing back for the ride home, I have the option to extend my route by up to 20 miles and be more comfortable in the more activity specific clothing.

Riding slow and easy on the way in defenitely helps keep the sweat factor lower.
The fan blowing at the desk/counter is a "must have" in any case.