I picked up a box of Exhibition Fiber 8.5 x 11 from Samy's Culver City, CA for my 3800 and am having exactly the same issue you are with the "micro cracks". I'm using the Pixel Genius ICC profile and following all instructions in the box and on the Pixel Genius site. There's a sticker on the back of my box with the number "700119" - who knows, that might be the batch number.
Although the cracks appear in every print I've run on this paper, they appear at slightly different densities and usually on either the left or right side of the image; not both at the same time.
Like dealy's experience, my 3800 prints like a charm on all my other stocks; be they glossy, luster, thick fine art rag, matte, etc. This is either a problem with the paper or instructions on how to print on it. Being I've tried all the suggestions users who aren't having problems with this paper have made and am still getting the cracks... my guess is there's a bad batch out there.
Here's the specs I'm using to print...
Epson Pro 3800 w/ clean print heads, purchased within the last week
8.5 x 11 Exhibition Fiber Paper
Tried both latest and shipped versions of print driver for OSX
Photoshop CS3 AdobeRGB 1998 ICC image profile
2880 Photo Fine
Pixel Genius 3800 EFP ICC Profile
Tried both Premium Lustre and Glossy settings
Tried both manual rear and sheet-feeder settings
Tried both standard and Paper Width of "5" paper types
Tried Black Point Compensation "on" and "off"
Tried Match Print Color "on" and "off"
Have "High Speed" turned off
Not letting the printer control any settings
... What a shame because, as far as I can tell, this would be the most amazing B&W print stock if it weren't for these ruinous cracks. For a moment I thought the artifacts could be intentional however there isn't a trace of them on the print samples at my local firstname.lastname@example.org