During normal monsoons, its very difficult to access many locations in Coorg. Coorg is a hilly region, and vehicles can have a hard time to be manoeuvred during monsoon. Be cautious before booking any hotel or homestay in a remote location during monsoons. It is advisable to stick to the towns like Mercara.
Currently its drought situation in Karnataka and many other places in South India. Coorg is the source of River kaveri and monsoons have been pretty bad this year(2008). Travelling this monsoon to Coorg should not be a problem.
The website https://coorg.com has a weather widget set, and travellers can check the weather there before making up their plans. Anyways, Anyhow Coorg is very beautiful in all seasons.
Though we had decided to stay at a homestay in South Coorg, we had to shelve our plans midway and ride upto Mercara, due to the rains. We didn’t have to regret because Mercara itself was beautiful and we had a great time.