I've been playing around with the EC2 for a while on OSX and Windows. On OSX it has some oddball acceleration issues. Despite being higher DPI than my MX518, it's covers less area at the same sensitivity. Also, while moving the mouse very slow, either something with OSX or the prediction (or a combination of the two) come into play and the cursor sometimes skips a few pixels no matter the mousing surface. It only seems to happen when the mouse is moving very slow (5 or 6 pixels per second tops).
On Windows, it doesn't seem to exhibit any of those issues. I don't have any jumping cursor at small speeds, and running at 2000 DPI seems about on par with my Orochi at 2000 DPI, just a lot smoother.
The mouse certainly is smoother in movement and feeling than the MX518, but not by a whole lot. It's definitely smoother than most laser mice I've used, which tend jump around or skitter at higher DPI. I do enjoy the buttons vice those on the MX518, G9, and all Razer mice I've tried (Mamba, Copperhead, Diamondback, Orochi). Very nice tactile umph and reminiscent of the Intellimouse. It also fits my hybrid claw/palm grip a bit better than my other mice -- enough of a palm bump to support my hand while not being too big to get in the way when clawing.
Thankfully I didn't have any mouse wheel problems like others have from the first batch. The wheel is thick rubber and puts up a lot of resistance when scrolling. Nice for games where you want a very tactile register, though it makes for scrolling longer documents and web pages fatiguing.
Overall, I kinda like the EC2 over other optical mice I've tried, even with the oddness in OSX. It's still not speed-twitchy like lasers, though it exhibits the smoothness that seems to be lacking in high DPI lasers but is common in opticals. Yet, it still maintains enough twitch-like response. I wish you could get some drivers for it to set up macros easily on the extra buttons (I use FRAPS a lot), but that can be worked around.
I wouldn't say the mouse is worth $60, especially when you can grab the MX518 which is VERY comparable for $35 or less. At $40 or less, if you like the older Intellimouse grip, I'd say it's a good buy.
Side note, the cord is freakishly long compared to other mice I have.