Just on TDP, it's a canon review site. he only reviews canon. any time he mentions nikon he says he doesn't own/use much nikon, if any.
For a canon vs canon vs canon-fit-3rd-party, it's great. every review he compares each lens to a few others in the same price/size/zoom range category, and explains the plus/minus of each, and who would want to be buying each one for what shooting style.
It's obvious he's got his personal favourite lenses (like the 70-200 2.8IS, frankly if i had his budget i'd probably never take it off the camera either).
For non-canon lenses it can be a bit of a mixed bag. It does seem sometimes he says a bit more often something like "i tried 4 copies of this <non canon> lens, every single one was different front/back focussing, one had bad centering, one the IS rattled and the other had a dead mouse between the elements". but more credit to him for trying out 4 and not giving up at the first bad one.
over at photozone.de, for some lenses that tdp says have bad QC, they say they loved it for all the QC reason tdp hated it. maybe they got one outlier? maybe tdp got 5 outliers? maybe there's a difference between the retail stuff they sell in the usa vs germany. all it says to me is to buy it in a shop and try it out, or online from a shop with a very good returns policy, and don't buy it the day before you need it.
tdp is sometimes harsher on 3rd party than canon. especially ziess, but if you've got zeiss money you expect good results so you have to be harsh. sometimes he says a 3rd party is not as good as the canon, but then says the canon is over twice the price and lets the reader decide if the next 5% in IQ is worth doubling the price. i've heard him be really harsh on canon lenses too, especially older kit lenses, moreso when there's a better 3rd-party for cheaper.
photozone put in the hard-yards too, MTF testing they try lots of bracket-focus shots, to negate field curvature, retesting if necessary, real numbers on CA and MTF i much prefer over tdp's sometimes-vague statements.
for cameras, neuro's already mentioned DxO mark for noise. if you're buying into a system from nothing then you also need to test the glass you have to buy. if you're already a canon-boy then there's nothing wrong with a tdp review. or even that, i'd just compare specs on canon.com and decide what features i need for my budget, there's not much choice in the top end, only in the xxxD budget range.
the one type of review that i do read are the user reviews from online retailers. but i also do drive a forklift full of salt and place it next to my laptop while i read. main point is that you never know the shooting style, subject, and quality-requirements of the reviewers, and you never know if they even work for whatever brand.
and whoever mentioned reading the negatives, me too. works for everything, i always went straight to the worst-rating picking accomodation at hostelworld when travelling, read through a few that just said 'it was crap' until i get to one that actually elaborated, then made a call as to whether it was the hostel, circumstances, or whether the reviewer was just a crybaby.
anyway, at the end, i'm with neuro. numbers don't lie, as long as you can trust the guy making the measurements and know the limitations that the numbers give...