How do you check if your RWs have already used beyond its limit? IS there any software to check the status of your RWs?

1. To what RWs are you referring?

2. To what limits are you referring?

RW - rewritable CD & DVD
Limits - How many time can it be re-used ( Erase and Burn again )

What should I look out for to know that it can't be used anymore? Is there a software for this?

According to http://www.answers.com/topic/cd-rw?cat=technology, a CD-RW has a rewriting cycles life (ca. 1,000). If course, the cheaper the disc the shorter its life span. Recommend using a USB flash drive. In the long run, it's less expensive for multiple rewrites.