MDS, I usually just lurk, I am a retired electrician and spend most of my time these days on genealogy and such, but seeing that no one is jumping in on this I will give my two cents$
It could be normal, electricity is a funny animal. Voltage is pressure just like hydraulics or water in a hose, if you shut it down or turn it on fast it will surge or draw down. You can have it checked by an electrician to make sure the amperage draw is within the proper limits of the appliances that are causing the symptoms you describe.
There are too many variables to give a definite answer, but if you feel uncomfortable, call an electrician and they can determine for you if it is normal or if there is a problem. Myself, I wouldn't worry unless you feel your electric bill is extremely high, or if the dimming is lasting more than a couple of seconds or accompanied by a growl when the condenser kicks in.
I almost forgot, do your lights flicker? If so there may be loose connections, call an electrician and have them check it out. See why I spend most of my time on genealogy, I forget things;-)