How to put this on few lines...
E-mail. You could use Thunderbird it works for Mac, MS and Linux. Evolution mail is just as good as Outlook, KMail is the other E-Mail client.
Office Productivity: You can use Open Office, is License free and works on MS, Mac and Linux.
Browsers: Firefox, Chrome, Opera, Sea Monkey and many others.
Accounting: Gnucash Cash and KMyMoney
Advantage over XP: No Antivirus to take care off, No Addware to mess it up, It has its own firewall if you wish to activate.
What does not have and that goes with any Operating System. Proprietary software that is written for that OS in specific (most games). WINE is like a MS emulator (for lack of better words) and Cedega that can you can run MS applications. by my experience is a 50/50 chance that will work.
I hope this works. 