[Mark.B]

For new sites I actually do recommend vB5, UNLESS you are looking to have a heavily modified site, in which case it needs to be vB4.

There are not that many 'major' add-ons for vB5, though the number of 'mini-mods' is slowly increasing. It won't ever reach the levels of vB4 though, mainly because it's much harder to modify.

Also remember that some external stuff in vB4 is gradually breaking - notably Facebook integration, because Facebook move the goalposts every few months and vB4 is no longer being updated with those kind of changes. I fully expect PayPal might end up the same way at some point, if it hasn't already (I don't use PayPal so can't be sure). There's also some minor niggles with the editor in some browsers but that can be worked round quite easily.