Attached Link: http://www.doschdesign.com/e_infobase

Scroll down on linked page to see a Texture Aging Tutorial that shows what great lengths some folks go to in order to achieve a realistic look (or at least a very distressed one!). I'm not much of a painter myself so I often try to bring in my wear&tear via photographs (combining multiple photos in photoshop using soft light can be very effective). I try to avoid "seamless" textures because even though the seam doesn't show(assuming the texture was prepared well) there will still be very obvious repeating patterns in the texture. I like to use giant texture maps (such as a high-res digital photo) large enough to cover the whole object without too much stretching. Even if you do use canned textures prepared by others I think it's good to know how to alter them (either in Photoshop or in post or with something like DCG's interesting new Noir plug-in for Carrara) so your work won't look just like everyone else's who happens to have the same texture at their disposal.

http://www.oken3d.com/workshop/creative.html is a good online texturing course that I took a while back. I've attached a picture of a wall that got some hand painting using a tablet in Painter 6 (I'm no artist but I do enjoy hanging out with them!) plus some photos of various distressed walls I took around town (original photos available at http://www.hcstudios.com/goodies.html).

The Texturing & Surfacing - General thread at http://www.cgtalk.com/ has some rather passionate discussions about texturing.

There seem to be at least three camps on texturing: the ones who hand paint every last little gory detail of their texture maps while hunched over their drawing tablet, the ones who run around taking photos of anything and everything and mix things together in photoshop and finally those who do wicked things using strictly procedural textures inside their 3d program (and it seems like Carrara is very good in this department since lots of mixing and nesting can generate some pretty interesting results; Litst's Real World Carrara Metals package sold here at renderosity has some good examples of complex procedural shaders).

To me it's the procedural approach where you really feel like the computer is doing a lot of the work for you but there are those who argue that procedural textures can never get that close to reality (and when done in haste they often look just awful and scream that the art was done on a computer).

www.dvgarage.com has some rather intense information about making things look realistic.

Something I read recently basically said if reality is what you're after then a camera or camcorder will do you just fine. Maybe the value of 3D is being able to put your own spin on things rather than just slavishly trying to make something that looks just like a photo. I think that professional photographers often wait hours or days for just the right light for their shots and in 3D you can whip up just about any kind of lighting scheme whenever you want (and it's interesting to me how many 3d artists like our own Toxe - http://www.eovia.com/carrara/user_proj_car_toxe.jsp - who stress the importance of lighting).

Enough rambling for one post. So far I think texturing is my favorite part of working in 3D (I still find lighting very difficult).