Question:
Go for the t-shirt (if you are wearing one).
It definitely has increased longevity for me since i've been doing so, and I havent stained one yet! No hugging issues either !!

Answer:
I do this sometimes, but only if the fragrance is a non-stainer!

Answer:
Yes, for weak fragrances. I've never had any problems with stains.

Answer:
Gucci PH stained my shirt

Answer:
I spray mostly on my skin and do just one on my shirt; possibly one on the jacket.
There ARE fragrances that will show up if sprayed on a light-colored shirt, but should wash right out. Two in particular I can name are Cafe Noir, which is very deep red, and Davidoff Relax, which is dark teal.
I would imagine that cologne would rub-off of moist skin more easily than it would rub-off of a t-shirt (onto someone else).
And I think you do get an extra boost by spraying the clothes a bit. It doesn't get burned off as quickly as on your skin, and the fabric holds the fragrance well, like a paper tester strip.

Answer:
No...waste in my opinion. No sillage. Unless you want to smell yourself. Sure people who hug you will smell, but you can get more hugs if you LURE them in with some sillage and people will know who is wearing that damn good cologne.

Answer:
A guy at work sprayed Tommy Bahama on my suit. I told him in no uncertain terms to never do that again. For some reason, that arm of my suit jacket smelled like Bois du Portugal for the next two and a half weeks. I like Tommy Bahama, but I don't wash my suit, and there is no way for me to get the smell out. Spray just about anything on clothes, and it's very tenacious. Plus, it'll smell like you are oozing the scent, and it has leaked through your shirt, which is a plus, so I'd give a thumbs up on shirt spraying when appropriate. I've never had it stain though... I'm pretty sure Genvy would stain, though I've never tried that one on a shirt.
Scentronic, bitchin' crocodile on your avatar, I'm a Lacoste man myself (clothing, not frags really...)
- Rich

Answer:
I spray on the skin. I did spray on my clothes a long time ago, but I found some staining. Also I find that at times when the body heat increases in the area of the spray, it intensifies the scent. Do not find this to be true when sprayed on clothes.