Rapidshare have implemented a new captcha for some time that asks the user to enter four out of x letters that have a cat (others have a similar looking picture of a dog with a smaller head) in the background. This new captcha is confusing to users and many have decided that it is not worth the trouble.

One solution is to wait for the so called Rapidshare Happy Hours which allow downloading without filling out the captchas and no waiting time if the servers can handle the download. Rapidshare Happy Hours are active between 0:00 - 18:00 UTC+1 on Mondays to Fridays and 0:00 - 14:00 UTC+1 on Saturdays and Sundays.

If you are a heavy Rapidshare user you might find the Firefox add-on Happy Checker useful which notifies the user when the Rapidshare Happy Hour is active. I think that it should not be to hard to memorize the Happy Hour times and download from Rapidshare in those times only without installing yet another Firefox extension.
(ye addon rapidshare happy hours active hootay hee notify kerta hai aur aap premium user ki terha download ker saktay hain.)