At least according to this, you must spend coins from the same address you received them on, so using different addresses doesn't buy you much. You still can't spend the BitCoins you've received and keep your anonymity. The page I linked recommends a procedure for money-laundering; I'm not sure how to evaluate how effective it is, but it's definitely inconvenient.
Inconvenience strikes me as a major strike against a traceable currency; I suspect it would be a lot more tolerable for an untraceable one. But both inconvenience and traceability, particularly if governments are against it, would be pretty bad for it.
Tangential, but a subject of some local interest:
Why Bitcoin will fail by Avery Pennarun. "The sky isn't red." Thesis:
I'm not sure I buy these and am not competent to evaluate his claims on 3., but would like others' critique.
L019: Bitcoin P2P Currency: The Most Dangerous Project We've Ever Seen by Jason Calacanis. A rather more enthusiastic viewpoint of the project:
The actual text contains many more caveats than the eye-catching selection of points above.