What do you limp?

There's been a bit of discussion recently about the benefits of limping small and mid pocket pairs with some people (whose advice I try to listen to) saying that it's a bad idea to limp these. Others have said that it's OK to limp them from late position after there are already limpers in the pot. These discussions have piqued my interest because I often wonder whether it is ever right to limp.

I'm wondering what people are open limping with. From early position? From middle position? From late position? Assume a full (or nearly full) table in early levels. If the chip structure makes a difference, I'm more interested in hearing about what people are doing at PS where everyone starts with 1500 in chips.

So, what do you limp with?