Upgrade 3.0.x to 3.5.x

[m3site]

Hi, I have site with 3.0 with custom skins and mods installed. Can I just upgrade to 3.5.x?

[TTG]

Upgrade may cause problems with your custom skin, check with designer.
Hacks installed for 3.x.x won't work with 3.5.x but most of the 3.x.x have now been converted for 3.5.x.

Might be a good idea to read this (http://www.vbulletin.com/forum/showthread.php?t=156385) and this (http://www.vbulletin.com/forum/showthread.php?t=158122)