I'd bet that you could walk for 90 mins even at a fast pace without getting all sweaty? If so then you can cycle for 90 mins without getting sweaty :)

Seriously though, I have 2 main modes of commute cycling: 1 as fast as I can manage, which I only do when I know I can shower at either end 2 at a pretty decent pace but one where I know that I'll stay cool and dry enough to not be a sweaty mess. Depending on the temp and how far I might slow right down for the last few minutes just to cool off.

The right clothes also help - even going pretty fast in lycra you'll stay cool enough. Cycling in full work clothes is doable but not fun for miles and miles.

Main thing for me was not carrying a bag on my back, as that makes me sweaty no matter the speed. I have a small bag for clothes on the front of my road bike (super cheap off ebay) and a rack on the back for bits. I try not to commute with a laptop - I've not needed to really so far.

It's a good question. In my climate, eight months out of the year it's impossible to ride for more than twenty minutes without getting sweaty, but I find that most days don't need a full shower to freshen up. Just take a washcloth with you, get it wet, and do a once-over when you change clothes. Re-apply deodorant and you're fine. There are still a lot of days (almost every day in the height of summer) where it's so hot that just being outside is enough to make you sweat, and after any significant time on the bike, you will continue sweating bullets even in the frigid office air conditioning while your body cools down. In that case, arrive a little early, work at your desk until you stop sweating, and then go wipe off and change. You won't smell bad while the sweat is fresh (as long as your bike clothes don't accumulate a vile odor — be careful about this.) Cleaning off before you stop sweating is a mistake.

Alcohol-based wet wipes are the nuclear option if you still have odor issues. Obviously they're not very green to use every day, but having some on hand can give you peace of mind if you're afraid you might unexpectedly need to go face-to-face with upper management or a customer.

Ease off on your pace for the last 10-15 min so your body has a chance to cool off. If you are showering regularly you remove the bacteria that cause the stank, so sweating by itself won't cause most people to be excessively funky.

I'm not the original poster, and I'm about to write something gross, but I commute for long times too and I find the sweat less of an issue than I originally expected (I do live in a climate that is not overly hot and humid, though). I avoid using a backpack (in favor using panniers) so that my back isn't all sweaty, and for the rest I find that the sweat dries up quickly and doesn't leave a trace. In the worst case I take a spare t-shirt and a deodorant stick.

On my morning commute it's not bad, because mornings are cool. If I put on a windbreaker due to the chill, then I get a little bit sweaty. Once I stop riding, the sweat naturally dries after a few minutes. I don't need a shower just because I perspired somewhat.

If I'm going down to San Jose I'm probably meeting friends at a bar or going to a show or something. Hardly the end of the world to work up a mild sweat and then my body dries after I stop, then as I start to feel a chill, I put warmer clothes on. It's not an issue.