A WebmasterWorld forum member decided to experiment with his title tags and made some slight adjustments. Consequently, he noticed a 65% decrease in traffic.
Is this the end for him? It's possible, as one forum member says:
Unless you are a super trusted authority site (ie you can throw up a page on a long tail and rank Top 3 in an hour), then Google is very cranky about title changes lately.
The particular forum member advises against changing a lot of title tags at once, as this could be very dangerous. WebmasterWorld administrator Tedster has agreed with this and says that Google is also sensitive to other changes, including keywords in the alt element and links in the footer (at least if it's a relatively new site which was launched several months before).
In this case, forum members suspect that this could be an over-optimization penalty.
It's best to make some decisions slowly before you do anything that can put your site traffic and rankings at risk.
Forum discussion continues at WebmasterWorld.