long winded, sorry!
Hate to say it, but I'm kind of glad to hear others are in the same situation as me! I've been looking at various message boards, and it doesn't seem like there are very many riders with full-blown asthma out there. Generally, people are really surprised when they find out I have asthma. My story:
I was never very athletic as a kid, and could never keep up in gym class because I would be so out of breath after running just 1/4 of a mile (the most popular PE class games, of course, always involved running). My teachers chalked it up (as did I) to being lazy, out of shape, and generally unathletic. The one sport I could do, however, was swimming (my first love). In high school, I started to have trouble breathing when I swam too, and then I really knew that something was up. Turns out that I have full-blown (ie: not exercise induced) asthma, aggravated by allergies.
After starting meds, I was determined to be more active (not one of those asthmatics that sits on the sidelines and explains "I have asthma"). I started running, biking, skiing, etc. Quickly gave up running (bad knees) and it's a bit hard to downhill ski in the midwest, but biking stuck. Unfortunately, the initial euphoria of the "miracle- drugs" wore off. I've tried a bunch of medications, but generally Advair and Albuterol work the best for me, along with Zyrtec for the allergies. I still get a hacking cough that lasts for hours afterwards riding in cold weather (even with the albuterol) or on hills (i die. i get dropped. it's okay.).
I do race, albeit not very fast (especially early in the season). I take a puff of the ol' inhaler about 1/2 hour before the race, warm up for about an hour, and concentrate on keeping my breathing steady. Albuterol makes me kind of jittery (like i just had a double espresso), and taking more than one puff in an hour makes me really dizzy, so i try to use it sparingly.
The first race I had to drop out (collegiate racing starts in February, even in the midwest) because i couldn't breathe, and it is incredibly frustrating to have your lungs give out before your legs! I carry an at-home nebulizer "just in case" (disguised in a cycling-shoe box

)... i hope never to end up in the ER, especially given some of the places we race!
I've also found that (during cold weather rides) heating up your water helps (warm water relaxes your chest- if it doesn't freeze 10 min into your ride). On any ride I carry a camelbak (even road riding), because as I breathe heavier, my throat tends to get sore, which aggravates the asthma. Water helps, and I drink more with the camelbak. Supposedly yoga helps (some claim "cures") asthma too, but I'm still looking into that.
it is possible to control your asthma enough to push yourself athletically, despite what my doctor keeps telling me ("don't exercise! you'll just give yourself an asthma attack! blah blah blah")

happy riding!