Did you know you can only have so much of a friends list in Facebook? Yes..the 5000 limit is the given maximum of any Facebook user that can connect and upon hitting 3000, the system will try to stop you from doing so, accepting new friends and such due to spamming and abuse of the system.
Being a developer, I find that the limits is a good thing but we tend to circumvent the system by harvesting the email addresses and connecting them and filtering through email address systems. Yahoo offers a great way to import the current user list with email addresses and then post export them into other services such as LinkedIn or other mailing list to make greater contact.
I have had over 16000 contacts over the past 2 years and that is a large sum, and pruning , triming them will keep the limits far from being breached and me from getting a red card from the administration. Overall, these connections are just actually, 400 over real people other than spam, game clones and such evil derived from Zynga's Mafia Wars and the like.
400 People out of 16,000 actually exist, with 1100 validated email addresses.So it's ok to prune occasionally but do import the contact list and mail merge them before hand. Having said that, LinkedIn is a great way to know people, professionally and not just plain kids on the block pretending to be 30 year olds.
Other than that, do have fun and keep your real friends who you comment and talk about on the lists.