The slide's image tone is not bad. It tends to be a little off (usually greenish), though sometimes its shifted slightly blue - purple. I've only done two rolls, one's been green-ish, ones been purple - ish, but I think that I have exposure relatively nailed down now. It should be perfectly black, as that's how it is if its developed normally as negatives. It's certainly superior to E6.
There are two issues, however. If the negative is overdeveloped in the B&W chems, and / or exposed to light after the 1st dev. for too long, there is a lot of what appears to be base fog evident across the film. I believe that this is not necessarily fog, but just REALLY exposed silver that develops so black that the blix can't bleach it all (good 'ol silver retention). In a process with a bleach, fix (both separate), I'd imagine that they'd come out much better. There tends to be a purple base which is not a good thing in slides. Drop the negatives in fixer after they come back from the lab (for about 5 min.). This clears most, if not all of the base stain.
One tip; if you try this, make sure that you wash the negative well before sending it off to be processed. It's not good idea to mix D-76 with the color developer.
I'll post some scans after Christmas break when (and if) I get the chance. Not e that this only works with Ilford XP2, not the Kodak stuff, as XP2 is the only clear - based chromogenic B&W film.
This also works with regular colro film, by the way. The result is "positives" with decidedly odd color and an orange mask. Not useful, but pretty cool.
[end long-winded discussion]