I'm a little biased

But I think the Primer is a great book and the Dying Earth RPG is fantastic.
I am the author of the Primer of Practical Magic, which I did free lance for Pelgrane four years ago. Basically I was such a Jack Vance nut when I found out they had the license for a Dying Earth game, I was determined to get involved somehow. Robin Laws had already done the game itself so I suggested doing a D20 book, and Simon was nice enough to humor me.
The Primer has a very different feel from DERPG, it's funny but it was written more as an attempt to re-introduce the true Vancian magic system to DnD in a kind of Gygaxian context, if that means anything. I think it's got a lot of great spells you can use for DnD, particularly low-level spells, I made up probably 20 new cantrips and converted all the hilarious, quirky spells Pelgrane created for DERPG. They are all really wierd and indirect, many are adventure hooks in and of themselves. Plus there are a lot of really bizarrely wonderful magic items.
To be honest the Primer was kind of tanked by reviewers, who criticized it for having balance issues with some of the spells, so keep in mind if you use it you may have to make some adjustments. But I liked it

It was kind of hard to reconcile the very open ended, 'fill in the details with your imagination' mentality of Jack Vance with the Balance at all Costs, explain everything to the nth degree mentality of 3E, but I did my best.
There was also a "Codicilliary" (errata) page somewhere with a lot of extras and a few useful corrections, I'm not sure if they still have it up, if you email Simon at Pelgrane I'm sure he could get it for you.
I love the Dying Earth Role Playing game though I've only actually played one campaign several years ago. Those games stand out in my memory is some of the most fun game nights I ever had. The problem for me is definitely in finding the right group. I usually play with non-gamers who can be a little too shy for all that role playing, but even among gamers and fantasy geeks, in spite of how cool the Dying Earth novels are, surprisingly few people I've met ever seem to have read them in the US (personally I think Jack Vances humor is a little too subversive for most Americans, Cugel the Clever is a far cry from Aragorn or Drzzt!). But I agree if you have a group capable of playing Paranoia you should have one who could 'get' DERPG fairly easily, I think it will really open up a completely unexpected and fun dimension to the Fantasy RPG genre. (Especially if you like low-fantasy and have a good sense of humor)
I think all of Pelgranes DERPG stuff is really good, my personal favorites are probably the little magazine they did (I'm biased here again because I wrote a few articles in them) called the Excellent Prismatic Spray. These have all kinds of terrific adventure hooks and funny, seditious little ideas that I have used in my regular / houseruled DnD games over the years with great success. If you want to inject a little truly unique, funny, and quintissentially old school (in a good way) feel to your DnD game, you can't go wrong with this stuff.
G.