Hate to ask such a possible dumb question but, I'm trying to buy the rain x latitude blades and I don't know what size blades would fit. Tried to find it in the manual but didn't find it. I even searched it online and couldn't find it. Does anybody know what size I can get? Thanks in advance

Just a guess on why . . .

To maximize the sweep coverage, as the 2 arcs work "best" with difference sizes.  That way, more of the windscreen is cleared w/ each sweep at minimal mechanical complication.  -For the opposite, complex mechanics, look at the variable length arms on Mercedes.  They physically shorten to clear the edges of the windscreen.  On my Miata, I installed ones larger than stock, but they loose contact on the far edge of the screen- which doesn't bother me in the slightest.  The result is a larger cleared area when running the wipers.
Scion/Toyota would have used 2 sizes and spaced the motor axles accordingly, so they would have max cleaning w/ minimal part complexity.

has anyone figured out a way to use a standard rainx blade on the rear?  or do i have to go to the dealer (ick)

The certainly have . . .
My 90 Miata was advanced back in 1989, but seems very old-school now, too.

I've always liked CJ5s (The main Jeep line from 1954-1983).  Should I ever get an offroader, a pre-square light Jeep would be near the top of my list (as would the older bodystyle Land Cruisers).

There is an alternative to going to the dealer for a replacement rear blade on the 2008+ Scion Xb's. It may first appear that the blade and arm are one piece but if you take a look, you'll see the wiper blade can be replaced and its actually quite simple. There may be other alternatives, but the 'Trico Exact Fit Rear Blade' at wipers123 online snaps right onto the special rear arm and looks like the factory original. Much cheaper than the dealer alternative. Comes with removal and replacement instructions too. Hope this helps.

Key Techniques is the answer.  http://scionlife.com/forums/showthread.php?t=117284

I got a plug, painted to match, for around $15.

Seems like a dumb question, but how do you get the damn wiper blades off?  I can't find anything in the owner's manual and I've pushed and pulled and pressed the rectangular tab near the middle of the blade.  Nothing.  The next step is to get really aggressive until something slips or breaks and leaves a big gash on my hand.  Cursing at it and calling it names relating to canine parenting hasn't helped. 

Also, I assume the rear window washer draws fluid from the tank under the hood.  Previous cars I've owned have had a separate tank in the back.  Again, nothing in the manual about that.

Bingo!  You need to take a screwdrier, pop out the little rectangular clip in the middle of the blade then just tap the end of the wiper and it pops off.