I've used the DG419 SPCO CMOS analogue switch a couple of times recently - one in a sample-and-hold circuit and the other in a PSR - and in both cases I've observed significant problems with the switches, manifested as significant DC leakage to the negative supply rail.
It turns out that all the DG419 parts we had in stock were Siliconix and the problem occurred with every part I tried. I then ordered some Maxim parts, (which incidentally have a better spec in terms of charge injection, on-resistance etc), and there is no sign of the problem with these parts.
Has anyone else experienced similar problems with the Siliconix parts?