How many characters are reasonable to have in a blog name (and in turn domain). How many do you consider to be too long? Is there a common standard of threshold that people stick to?

In my own opinion as long as it is Short and concise, then you must go for it. Short Blog names are easy to remember.

64 characters is too long because hostnames (domains) have a maximum of 63 characters.

From RFC 1034:

The labels must follow the rules for ARPANET host names. They must
start with a letter, end with a letter or digit, and have as interior
characters only letters, digits, and hyphen. There are also some
restrictions on the length. Labels must be 63 characters or less.

It seems no requirement,but just easy to remember.

It'll be too long if your blog name is more than the maximum number if characters you can only use.

The shorter the better and easy to remember.

Finally, and it's even better if you can put a keyword.

Originally Posted by fatasy

It seems no requirement,but just easy to remember.

I recommend you to use your keywords as your blog name for this got an advantage on you.

choose a name that is easy to remember...

Easy to remember names are the main factors in increasing returning visitors.

Short domain names are always better. Use some popular words of your targeted niche, they are easy to remember.

When selecting a domain name, I'd suggest you worry less about stuffing it full of keywords and worry more about it being short, easy to remember, easy to type, easy to say. It's the one URL on your site that users have the BEST chance of remembering.

It's the one URL on your site that users have the BEST chance of remembering.

Well, no doubt to that. Short words are easy to remember and easy to to retrieve.