What can I do to help longevity/sillage?

I'm a bit surprised!
Obsession, D&G and Pi don't last on your skin?
These are usually great sillage scents.

Maybe your skin is very dry?

Where do you spritz it on your body?
How much?

Or maybe your nose rapidly forgets or get saturated with the scent ans simply ignore it after a short while?

On cooler weather, the skin gets generally dryer. Dry skin is not a friend of scents/fragrances so I often apply an unscented body lotion right after I shower. Another thing I do is I layer my fragrances with the shower gel, lotion or powder. For instance, when I know I'll be wearing Frederic Malle's Vetiver Extraordinaire, I would use the shower gel Vetiver Extraordinaire. Try it!

Any old unscented lotion will work just fine, if an ancillary product isn't available. But I do want to note that sometimes it is just the perception of the wearer, or it has something to do with how potent other scents are by comparison. And body heat, and climate, and so on. Many people put a spritz on their clothes, but if you do that be ready for it to mix with the scent you wear next time you wear that unlaundered shirt.

Could just use the ol' Thrax method and put quite a bit more on.

So Pi and Obsession don't have strong sillage on you?

Try spraying you chest as well.

I've sprayed the back of my neck at times, and that seems to really project.

The Pres. of Creed US sprayed once on each side of his neck - is that what you're doing?

As for dry skin, try jojoba oil. If you do, apply sparingly at 1st.

Either side of the neck? That's what I've always done -- pulse points on wrists and legs always come after the neck with me, and the sides of my neck get scent even if nothing else does. Works beautifully for me.

Don't understand about D&G and Pi, as those are two of the strongest scents (both in terms of sillage and longevity) that I own. Oh, well -- each person's body chemistry is so different, and (as someone else pointed out earlier), climate can make a huge difference, too.

Try Lagerfeld Photo if you want a long-lasting warm scent for cold weather -- Photo's one of those scents that lasts and lasts and lasts and lasts and then lasts some more and then lasts for good measure . . . .

Either side of the neck? That's what I've always done -- pulse points on wrists and legs always come after the neck with me, and the sides of my neck get scent even if nothing else does. Works beautifully for me. It also works for me to apply my scent under my arms, just after any deodorant (ancillary or not). In very mild weather, I might not even put on deodorant, opting instead for a spritz (or daub) of scent only.

Can't empathize with your experience of D&G and Pi, as those are two of the strongest scents (both in terms of sillage and longevity) in my wardrobe. Oh, well -- each person's body chemistry IS unique.

For example, my other half tried on Gaultier² today shortly after I did. (That was around 1 P.M., just after we had left an 11 A.M. showing of the hilarious Borat.) I can still smell my Gaultier² spritz on my wrist, and it's now 11 P.M. here. HIS spritz of Gaultier², though, first started to fade around 3 P.M., and had faded completely by 5 P.M. (Go freakin' figure!)

Try Lagerfeld Photo if you want a long-lasting warm scent for cold weather -- Photo's one of those scents that lasts and lasts and lasts -- and lasts. and then lasts some more. and then lasts a while longer just for good measure . . . Seriously, I love Photo SO much, but seldom wear it simply BECAUSE I can't get it to away without a serious shower and at least 8 hours of sleep afterward. (And even then, I can still pick up whiffs of it the next day. Kouros is often the same way with my body chemistry, as are M7 and Erolfa.)

My skin drinks up scents too, especially in cold weather.

Half a dozen sprays of just about anything is my minimum, I'm finding - and still I can only hope for 3 hours.

Just get A*men and your problem is solved.

Seriously though, you might be a little too conservative with your application methods. Try applying at least 6 sprays and then tell us how long it lasts on you.

I have a similar problem. Apparently my skin doesn't help.

Just last night I put 6 spritz of CK Eternity and about one hour later I checked with my GF and she coudn't even detect it. :O

And I live in a very hot, humid city...

Oh well.

It's also good to wear an "unscented" waxy cream/pomade and/or dry oil on your skin before spraying and then spray your frag over it, it will make it last much longer.