I'm a new WP blogger. Sometimes I cannot tell if a comment is spam or legit. Same with respect to trackbacks

First Comment: The author field = Domain Names: Federal Court or UDRP Arbitration? | KEYTLaw « Blogging. Email field is blank. URL field = http://eamico.com/?p=36006. Text of the comment = [...] Read more here: Domain Names: Federal Court or UDRP Arbitration? | KEYTLaw [...]

The comment is for a post located here:

http://www.keytlaw.com/blog/2009/10/cybersquatting/

What is this? Is it legit? Should I delete or approve it?

Second Comment: The author name field = Twitted by azattorney. Email field is blank. The URL field = http://realurl.org/twitted.php?id=4736217813. Text = [...] This post was Twitted by azattorney [...]

FYI. My Twitter account is azattorney. All of my blog headlines are posted automatically to that Twitter account by a plugin.

The comment is for the same post referred to in question 1 above.

What is this? Is it legit? Should I delete or approve it?

I make people register and I use the akismet plugin.

Spam is in the eye of the beholder. To the 'spammer' their coment is an ad, to me it's spam, but in the end I have to make the decision on my blog, you have to make it on yours.

I use Akismet. It marked the first comment as spam and the did not mark the second as spam. I'm just not familiar with how a ping or trackback looks or how to distinguish a ping or trackback from a comment.

Nor do I know why I got the reference to my Twitter account name. Was that a reTweet or a mention in somebody's tweet or did somebody manually enter the info into the blog's comment area?

You got the second trackback because you are automatically posting a copy of the posts URL to yoru twitter account. Most likely you will see this same trackback for all of your posts the only difference would be the titles and times.