Bill Brown levels a really good complaint about the lack of standards around what I call tag punctuation: the delimiters that are used to separate a list of tags:

[from Tag formats: Can't we all just get along? - Signal vs. Noise (by 37signals)]

What if I want to tag something “white house” instead of with the separate tags “white” and “house” (which changes the meaning) or “whitehouse”/”white+house” (unintuitive)? Enter comma delimited tagging.

He goes on to list a variety of services -- Flickr, Amazon, 43Things -- and there is little consistency.

At Technorati, I use "+" to tie words together, like "compound+phrase", because I am creating the tags in HTML URLs, and blanks don't work well there, but T'rati changes the plus to a blank. Some services won't allow plus signs in tags, which is a pain. Some people use "wikiword" style, with all the words smooshed together.

It would be good if a standard emerged for punctuation, so I propose the following:

1. All tag solutions should allow blanks and other special characters in tags except for comma. [Then I could forego the use of "+".]
2. commas should be used to delimit tags in a list.