It is it safe to upgrade my ipad 2 w/ios5.1.1 to ios6 ?

I had no problems whatsoever. But be smart about updating and be proactive. Whether you update OTA via WiFi or use iTunes - take the steps necessary to ensure that you will have everything saved.

What you should do anytime that you update the device is to transfer purchases from the iPad into iTunes - File>Transfer Purchases - and you should backup the iPad as well. When you update the update the device, if something goes wrong, you can restore from the backup.

However, iTunes should ask if you want to backup before you update, but just in case create the backup yourself before you update. The backup contains your app data and settings - along with other items - so make sure you backup first.

If you have any other important files, you may want to transfer them to your computer as well, prior to the update.

Transfer purchases.

http://support.apple.com/kb/HT1848

How to backup and restore from a backup

http://support.apple.com/kb/HT1766

it should be no problem, i updated my ipad 2 yesterday and it works fine.

as sayed by Demo, make a back-up of your files, and before downloading: try to make as much space as you can (by deleting old files, replacing your ipad-made photos onto your pc and/or deleting not used programs), this will slim the change for your ipad to get stuck in the process.

altrough i like the update myself, be sure you want to update, because there will be some changes in interface and in the functions.