AbdulAlhazred
Legend
The "real" answer to that is, of course, as long as you want it to. There are ways of setting such things up locally, at least as far as the compendium goes, and by now CBLoader is quite widespread. Also, Masterplan. If 4e DDi support goes the way of the dodo, perhaps the power2ool guy ( @doublewumpus ) can be convinced to release a "home version" of his popular and useful webapp. I'd even pay for the privilege.
Yeah, I've looked at various options. As a happy non-owner of a windows license none of these options have been too useful to me (of course I have to do some jumping through hoops to do CB as well, and MB, but I don't need them often as a DM).
No doubt some portable tools can be created, there are some things like iplay4e that have done a fair job of it here and there, but we still lack a really good solid cross-platform 4e support program.