IntegraMOD

The Activation email for new users does not always get sent out, I have to head to the acp and inactive users and manually send the email something. This happens to on average 10% of new users.

Any ideas?

more than likely, it is their email filters. Most email clients are hypersensitive to your severs dns settings which is the reason most forum software emails get dropped, or sent to the junk folder.
http://dnsstuff.com has alot of good info for troubleshooting email problems.
Since your forum is sending some emails, it is not likely that the problem is in your forum, or forum settings

I had the same issue. I had to manually activate them each day.
I just set it up so no activation was required.
Going to true it like that for a while and see.

Yes, Ive had that issue as well.
On one host the mails always went to Junk folders, on another host no mail at all was ever sent.
So to avoid it all I disabled email verification, and made my forums so that only registered members could post or reply.
So basically you still have the control to ban by IP, and cut the spamming threat out 99.99 %

Personally I think its smarter this way, I know I hate having to wait for an activation email.
Either way it goes once they become registered, you now can IP track them

I don't have the spam trouble, the emails just don't get sent.

When I go to the inactive users list in the ACP, is the the amount of emails sent is 0

Then its a good chance its your hosts settings then.
As mentioned its smarter to avoid the hassle and the possibility of losing new potential members by just configuring it to allow members to join minus the email verification.
I made the switch close to a year ago and virtually eliminated the worry of whether or not new registrants ever got their verification email.
Wont hurt to give it a shot.