Here are some threads you can read to help you decide.
http://www.aximsite.com/boards/showt...ghlight=update
http://www.aximsite.com/boards/showt...ht=rolled+back
http://www.aximsite.com/boards/showthread.php?t=146233
http://www.aximsite.com/boards/showthread.php?t=146243
Just like Tblove has said, many have rolled back already. Just my observation, there are only a few who are "actively" (take note of the word actively) recommending WM5 for the X50. Some of them have suspiciously low post count (as in less than 5), one of them cannot make 2003SE to work and needed to do a "HARD RESET" everyday (everyone knows 2003SE is a reliable OS for the X50 but his problem might be legit), the other has his X50 on ebay and one posted in this thread.
Again, this is just my obvervation on the posts that I've read and I'm no way stating my opinion regarding WM5 for the X50 since I didn't upgrade my X50V to the new ROM.