I just broke the plastic piece off of the metal part of the metal shaft. I've been looking everywhere for a replacement stylus. I ended up calling Sony and the replacement part was on backorder as of April 24, 2011. She said it was 3-4 weeks for both the pink and silver stylus. She quotes me $62 for the stylus! The only way I can make sense of why it's so expensive is that it's made out of high grade NASA-made plastic and adamantium (I say this sarcastically).
Hopefully somebody knows of a good alternative than paying for the high price of these Sony styluses.
I did a search for some other places to get a replacement stylus:
Partstore.com - $18.19
http://www.partstore.com/Model/Sony/Sony/PRS600.aspx
Serviceplus.com - $14.99
https://www.servicesplus.sel.sony.co...A1732038A.aspx
Hope this helps.
The part number is exactly what Ken 401 said: A-1732-038-A