compatibility of the mod on the forum
 

I recently do a migration from VB3.8 to VB 5.1.1 .. And I would to say if the mods developed for vBulletin previously the version 5 on the forum are compatible with this version or no. Thanks

No, you will need to search for updated versions for vb5. most have been for vb4 and some for 5, it's still catching up. But, bottom line, you will need to find the updated versions or mods that are close to what you had on 3.

No single previous mod will work. Before updating, you should read the threads in this forum to make an informed decision, and you should take a look at the vB5 addon fourm and compare what (and how much) has been developed for vB5 since it was released well over a year ago.

thanks a lot!.. But I would like to ask you anothor question: if you should do a migration from vb3 to vb5.. what are the main factors that you can make that decision? (I use vb for a forum)
I read this page http://www.vbulletin.com/docs/html/vb5_intro_whatsnew but I want to know your opinion and experience!

vb4 is the current best. I still have to meet one single soul happy with vb5

I would never make that decision. Just do as I said and read up in this very forum, as I said.