I just started up my blog a couple days ago. Currently I have it (wordpress) set to force users to register and log in before commenting. I did this mostly because I don't want anonymous, garbage, posts. I'm afraid, however, that this is detering people from leaving comments. I was curious as to what everyone's preference was on this matter. Do users have to log in to comment on your blogs? If not do you get any spam because of it?

We just have the same concern. But for me, I still choose to moderate first the comments. I doesn't matter to me anymore if they don't leave comments at all since I am already sold with their visits. It's better this way since there are really a lot of spammers who's trying to inject unrelated links on your ranked pages. Just lately, I moderate a comment that looks like a sales letter or is a sale letter. I was just so thankful that the sales letter didn't appear on my blog. But I think this case depends on the niche of your blog.

I used to allow anyone without registering to leave comments, but I noticed that I get many spam comment, something like between 30 to 70 spam comments daily and very little good, relevant comments. I need to clear/moderate the comments and it is very time consuming. After I move to a new host, I decided to introduce spam control like make people register first before commenting and also use Akismet Spam plugin to control spam and so I don't have many comment left by people.
But, I think it is good that you can control this, else you got to waste your time clearing the 'rubbish'.

I think its the a nice way to avoid spammy comments, but still you can moderate all the comment even though you didn't force them log in for commenting purpose

Thanks for the info. For the time being I've decided to allow unregistered users to comment, however I installed the reCaptcha plugin that I think will stop automated spam for the most part.

If you use a spam blocker you should be fine, and you probably are deterring most of your visitors from commenting. People don't like to signup for things, especially if their only visiting your blog once.

Subscribing is more for repeat visitors, commenting should be for anyone. Even if you do get a few spammy comments with a spam blocker (I get very, very few) you can easily manually delete them.

before i allow blog commenter's to comment on my site without logging in.. but same as you are experiencing... i let them login first before commenting on one of my article... getting rid of spammers...