The idea has been put forth that we should visit our son in Thailand next November. Any hiking suggestions? We will be based in the north around Chiang Mai/Lamphun, but will probably see much of the country while we are there, if we are able to go.

Any suggestions for worthwhile trekking, camping, outdoor events would be welcome.

I was there in Dec 2006. The trekking areas are hard to get to via public transportation so everyone takes a tour. I had fun with the hike, overnight in the villages, whitewater rafting, and riding the elephants. Kind of commercial, but maybe your son has transportation and local knowledge?
Check www.lonelyplanet.com for Chang Mai guide companies. There are many companies with many trips. Book when you get to Chang Mai. The further distance away (like Bangkok) you book the more you will pay. They will do better than the 1st price they quote especially with a group.
You'll pay more to book thru a travel agent as well.
Sorry I can't remember the travel group I used.

Yeah, my son has been there teaching English and now is getting his Masters degree at Chulalongkorn Univ. in Bankok. So he can speak Thai.

(Side note. He learned not to walk in to an apartment manager and ask about apartments. They always quoted him higher rates than what he saw advertised. So he would phone first, verify rental rates and then walk in. Then they were stuck and couldn't charge this obviously non-Thai blue eyed blond haired guy extra.)

I'm just looking for people's responses to what they enjoyed. Then my son can figure out how to do it. He's gotten into the local scene pretty much. He even has his official elephant driver's license (Three days of study for the first level!).