Some comments deleted

When someone comments on my blog, I make sure it's not spam and then I allow comments to appear on my blog.
My blog is getting over thousand spam comments every week and while deleting such comments today, I deleted some of the genuine comments by Manish, David Urech, Dinesh and Gaurav. By mistake some checkboxes left checked while deleting commments...MT interface sucks :(
Guys, please don't mind and keep commenting here. I am thinking of ways to stop this approval-kind-of-process and let comments appear as soon as they are posted.
Any suggestions and guidence to stop this comment spamming are welcome.