Does Kenko make good tubes? I have the 70-210 f4, it technically does macro but at a 1:5 magnification and only at 210 - one of those 'barely a macro' macros. So, rather then spending the extra money to essentially get something I already have in another lens, just bringing a little closer, should I get extension tubes? So long as the AF remains in tact, there are no other problems?

Here is the link to the one I am looking at, but I am open to other ones that are better of course... - link (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=260255282133)

I have a set of Kenko tubes for my Canon EF mount gear and I love them. The AF is retained when I use them, but I usually turn it off and focus manually. You will want to do the same. When you're shooting macros your DOF gets pretty shallow, and manually focusing gives you a lot more control over what parts of the image are in sharp focus.

The link you posted is for a single tube. Do they sell them in a set for your system? I got a set of 3 for mine, and I love the versatility it gives me. Many times I will stack all 3 together to get real close.

Thanks for the input! What magnification would you say that your tubes bring you to? Also - would it cripple my infinite+ focal distance? If I'm shooting distant objects, would I need to take my tubes off?

would it cripple my infinite+ focal distance?
Exactly. Because it moves the lens further forward, you can't focus to infinity.
If you still want to focus to infinity - buy a macro lens, that does both.
If you just want to shoot macro - buy extension tubes.

If you can, buy a complete set, not just one tube.
Different lenses will give you different results.