It's supposed to be a phenomenal ride. I'd buy one in a second if I could find my size, near-new, for a good price. Unfortunately, it seems to be a favorite for scammers on eBay, so be careful of what you buy.
Differences vs. the 06 SJ Pro:
-Enduro has 130 mm travel vs. 120 mm on the SJ. The 2006 S-Works Carbon SJ ($7100) does have 130 mm, but all the aluminum SJs are 120.
-Geometry is a little different, partly just b/c the 2004 TALAS fork was 125 mm vs. the 2006 TALAS with 130 mm. HA on the Enduro is 70.5 (though swappable to 69.5). It's 69 on the SJ at full fork extension.
-The brain is different (and imroved) this year. The 2004 brain had adjustable threshold, meaning you could set the size of bump it takes to pop open the inertia valve, but that meant that any change you made to soften the small-bump compliance was impacting the pedaling platform. In contrast, the 2006 brain fade shock lets you adjust the low-speed compression damping from very soft to firm. That means the threshold for opening the inertia valve doesn't change when you adjust the small-bump compliance.
-Finally, the SJ is a bit notorious for having a low BB. It makes it rail corners nicely, but you donk your pedals pretty frequently. I'm pretty sure it was higher on the Enduro (but lowers if you change the linkage to the 69.5 HA setting).
If you're not an MBA-hater, here's a link for a review on mbaction.com:
http://www.mbaction.com/detail.asp?id=984
There's a more thorough write-up in the mag, which I've seen scanned and posted in this forum. Dig around and you'll find it.
Good luck...
-stads