I have the porter cable great machine came as a kit with two bases a plunge and a fixed, a dewalt, both take both 1/4 and 1/2 bits, a old commercial Black and decker, very similar to the dewalt but only 1/4 bits,
I gave the crappy sears thing away to some one who was desperate, for a piece of junk, (it had horse power but the shank was less than 1/2" and would only take 1/4 bits it was bulky and base was hard to adjust, and the base plate was stupid in design and would catch on things as it had three fingers that held the collars,
also have porter cable trim router, it only takes 1/4" bits,
the trim router are great for much more than just laminate counter tops, there a great tool for many other routing jobs, light small, and good power, with smaller bits,
the porter cable and the dewalt and B&d all take the porter cable collars,
you can buy cheap and it will probably get you buy but if you want some thing that will last and be worth something in a few years buy a good unit,
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as far as ply wood goes find some thing that has a number of plys, and is not filled with voids, many times the "hard wood" plywood is much better than the fir ply wood,
in our area there is a ply wood sold called "super ply" it is not really cabinet ply, in the since that it has a generic hard wood top veiner, on it, but it has water proof glue, and a good number of plys, (varies as to thickness) and there are not voids in the plys,
for doors the MDF core can make a nice door, as the core will take a nice stain,
http://home.att.net/~waterfront-wood...es/Plywood.htm
http://www.taunton.com/finehomebuild...ges/h00016.asp
stay away from particle board crap,
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but the truth of the matter is plywoods really do not machine well. you can do it but splintering and chipping is not uncommon,
some times you can minimize the chipping by "routing backward IN sted of pushing against the force of the bit, pull it with control and it will cut into its self and not be pulling on the fragile grains of the wood,
i have a port a cable but if i where doin cab. doors i would buy a craftsman with the routor table it will make life a lot easyer and would be cheaper than getting just a port a cable 
(wait till u see a combo on sale) 
The motor in it was/is fine, the plunge feature was only uselful for one project otherwise it caused more problems than it solved. You can get a Portor Cable PC690 for about 30-40 $$'s more than the Ryobi and every accessory known to man is made to work with it 
What I also like about the Portor Cable (and I think a couple of the other brands mentioned) is that you can buy an plunge base to go with it, so you get the best of both worlds.
