[cellarius]

As to the compatibility of mods: Not a single vb3/vb4 addon/modification will work on vB5. Not only will the underlying code be all new, but also the plugin system will work differently. This has already been established by Paul.
Still, I don't see how this can be avoided. You can't ask for an all new and modern codebase and expect old addons to work with it.

Regarding jquery: If anything, it will result in faster page loads. Now we're using two different JS frameworks plus a whole lot of custom vB JS. Better to use just jquery. If pulled offsite from google, chances are very high that the library doesn't even have to be loaded but is already present in the users browser cache from prior sites he visited.