A lot of people aren't making the switch because they wonder if their favourite applications will be available.
However, as of August 2007, the short answer to this generic question (can I run X application under Linux?) is most likely yes.
The development constraints of Linux are lower than for commercial OS's.
And the developer pool is virtually infinite : anyone can contribute.
This has led Linux to major improvements in the past years, towards more usability, and some flavors are now
comparable to their commercial counterparts in terms of usability.
So, in most cases, you can find a Linux counterpart to an existing application which will feel very familiar.
And in many cases, you can run the original Windows application from a Linux software "wrapper" like Wine, which embeds "enough of Windows"
to allow applications like Photoshop or World of Warcraft to run in Linux.
(to edit) add links to other relevant faq information (/to edit)
