I read http://grammarist.com/usage/muchly/ and it appears that this word is regarded as obsolete.  I and many of the people I know use the word regularly, however, frequently in situations where it would seem to me 'much' would be incorrect.  Examples:

Thanks muchly for the insightful gift!

He was muchly peeved when he found out what had happened to his car.

Are our usages acceptable within 'Standard English' (ish)?  How common is formal use of the word?  What about informal use?  When did this word *stop* being normal regular everyday English?