I did a good amount of research before I bought my X3, and decided the RF clones were too heavy for me to keep in my current living situation, decided on the X3. In the future, I might consider one though.
Heres the thing, For ~500 dollars more than the cost of my X3, I can get a lot more mill. This bothered me quite a bit, I was really wanting an RFclone for that money.
The quality of the X3 was impressive, far better than I had expected. Spindle runout was not even 2 tenths. I checked this mill for everything I could, I found it to be very accurate in the critical dimensions. THis was using a .0005" graduation DTI.

So my question is; Does an RF clone deliver similar quality? How have people found the accuracy of the mill in the critical places?

Hey Phantom, I too did much research on the both the x3 and the zay45 and found that for the money the zay 45 was the bang for the buck, but for the ease of moving a mill and shop space the x3 was nice in that respect. I think the bottomline is the part material and size that your working with should determine the mill you want to buy. Me my self I prefer to get the Zay45 but in my situation I plan to be purchasing a new and final home within this year and decided the Zay would have to wait so I only need to move one time from the store to my shop, in the meanwhile I built a manual mill http://www.cnczone.com/forums/showthread.php?t=18992
that I consider an X2 1/2, its beefier and more travel than the x2, and plan to beefit up more and put a bigger table on it, so I might end up being satisfied with it. But I think ya did good with the X3, looks like ya can cnc it fairly easy. Heres a link to a page where this guy has an x3 http://www.thms.tedatum.com/
The Hobbyist's Machine Shop

Yea I've seen that page.
I guess I was just thinking, for ~1000 dollars I got a pretty accurate machine. But these RF45 clones are so much bigger for 50% more, I'm just wondering what the quality is. I recall reading a post about the industrial Hobbies mill where a guy says his quill is .020" off center.

oooh damn thats alot .020 !!! But I sure do like the Industrial Hobbies one, nice with the bigger table, at the end of August the machining class starts here at my local community college, I,m hopin they,ll let me bring a big 'ole chunk of gray iron in there so I can mill me a bigger table for my mill and hopefully the 1/2 x 8 x 26" steel that I want to use on the sides to beef it up. I wish the X3 had a little bit bigger table , that was the only reason I gave up on it. I,m kinda diggin building the mill and figured I would build another one if I had a big enough mill to use.