I, respectfully, disagree that members registrations should be deleted simply because they don't post within 48 hours. There can be any number of reasons for not posting... maybe they are shy, maybe they don't have anything to say right now, maybe they THINK they need to register to view posts... whatever the reason, deleting them so quickly for not posting is just bad practice - however I do agree that deleting old, inactive members is good housekeeping (and keps your DB size down) - more about this later.
Now, RE: SPAM, as I've said a few times before in this thread, install the 'Stop Forum Spam' add on to the board - it will reduce SPAM to almost zero !
I'm a web developer, eCommerce manager, managed services provider, and forum admin... I had a problem for a while where one of my (successful & pretty busy) boards was constantly being attacked by spammers... I had IP ranges banned, email domains banned and various words banned - but they still got through, because I couldn't (manually) keep the blacklists up to date quickly enough. Then I installed SFS, and now I get almost zero SPAM.
'Stop Forum Spam' is a free, 'open', community-based and community-contributary SPAM fighting machine. It works like this, install the add on - this will then check EVERY new registration against a community maintained database of known spammers. It can be configured to check username, email address and IP address, or any combination of those - if it gets a 'hit' it will flag the registration and leave it sitting in 'Requires Approval' status. A mod or admin can then review the registration and accept or reject it.
Admins can also flag previously unknown spammers and get them added to the database, they can check registrations and search the SFS database for further information on that particular spammer - it'll show how many times they've been reported as a spammer, different email addresses and usernames used by an IP address, or different IPs used by username/email addresses.
It can also be used to check an existing membership list to weed out any 'sleepers'.
Anyways, this is my tuppence on this, and for the last time:
http://www.stopforumspam.comOne other quick point about maintenance, what I do is from time to time is delete members that have registered but never logged in, or have registered but not logged in in the last 180 days. You DO get people that register, check something, then disappear - but most of the time, they are spammer sleepers.
Again, just my tuppence