I do not encourage you to trust everything you read there as this will most likely make you paranoid (you might want to go ahead and see the poll results to get an idea how much penalty discussions worry webmasters) – but watching others share their experience and comparing it with yours is a good way to avoid Google disasters in practice.
The most recent thread there lists a few penalty related observations worth discussing here, I guess. Is it possible to tell a manual penalty from an automatic one and how can they be different? Of course, no one knows the exact answer but the thread participants’ observations should be paid attention to:
|Manual review||Algorithmic penalty / filtering|
|Penalty causes:||Manual penalties are usually related to off-site over-optimization, i.e. aggressive link building campaigns||Algorithmic filtering usually takes place with on-site over-optimization.|
|Penalty symptoms:||Ranking changes effect the whole site (though it can be also the sign of automatic one).||Only a few of site keyword rankings were effected.|
|Penalty removal (after the penalty flag is cleared):||A manual penalty might only be removed in slow steps.||An algorithmic penalty is often removed automatically; it can also be removed with no apparent reason “except that a lot of time passed.”|
One more good point to consider (for new sites): if you are sure everything is ok and you have never broken any rules but still suspect you were penalized, don’t rush to submit a reconsideration request – which might basically mean that you admit you were guilty of spamming even though you agree to be good from now on. Just give it some time (a couple of months probably) and you will see increased ranking again.