We are going to upgrade a 4.5 installation in order to get friendly url and other things. It is possible that the customer wants to upgrade to 5.x before two years time. Anyone with experience on issues when upgrading from 4.5 to 4.6 or directly to 5.x? Should we skip 4.6 and go straight for 5.x?
you cannot "skip" 4.6. In order to migrate (not upgrade) to 5.x. you first need to upgrade your site to 4.62B.
The next step is then to start Migrate to cms 5. Personally I think it would be best to go direct to latest version of EPiServer CMS (R2 coming next week). But it all depends on how much time you have to do it. Upgrade to 4.62B is quite fast, but migrate is more work.
Search EPiServer World on "migrate" will get you some usefull articles, technotes, blogs, forum posts etc. about migrate issues, hints, tips...
Also, this article is a start: