While I'm NOT suggesting that reusing plastic bottles is any more dangerous a practice than using them in the first place there is some reasearch that suggests that some of the things in packaging may be harmful to us. I can't put a link in cos the article is no longer there but here's a bit I found some time ago for a women's group I am involved with:

Turn Your Home Green
(Article taken from the Daily Express, Monday February 24th 2003)

Many cleaning products, packaging and even bedding can have a detrimental effect on your health and the environment. But you can buy green alternatives that are just as efficient and won't harm you or the planet, reports FRANCIS IVE

OUR BODIES are in contact with more manmade chemicals more than ever before. They are in everything from washing powders to hygiene products and spill out from our homes to pollute the environment. They can affect our skin, cause breathing problems and disrupt our hormones. These chemicals can build up in the body and some have been identified as endocrine disrupters that can affect our hormones.

There are now many safer alternatives, which Friends of the Earth (FoE) is keen to promote. Boots, Marks & Spencer, the Co-op, B&Q, IKEA, Early Learning Centre, Homebase, Argos, Debenhams, Body Shop, Mothercare and Sainsbury's have already signed the FoE's Risky Chemicals Pledge. They have agreed to phase out products that contain these chemicals and pressurise manufacturers into doing the same.
Here are some changes we can make to create healthier and greener homes.

YOU ARE WHAT YOU EAT
Dr Marilyn Glenvilie, author and expert in women's health who practises at the Hale Clinic in Central London, says there are 3,900 brands of insecticide, herbicide and fungicide approved for UK use. Some fruit and vegetables are sprayed 10 times before reaching supermarkets. "Eating organic food is one way to avoid these chemicals," she says. Organic food is available in supermarkets. It is also delivered by local box schemes such as SimplyOrganic (www.simplyorganic.net)

REMOVE THE WRAPPER
Most plastic packaging contains harmful chemicals. "Don't store fatty foods such as cheese or meat in plastic wrapping," says Marilyn. "Xenoestrogens, which are synthetic oestrogens in the plastic, are fat-loving and migrate into high-fat foods. They can then interfere with your hormones."
It is also best to avoid microwaving food in plastic containers as this intensifies the effect.

HELP THE ENVIRONMENT
Cleaners, polishes, laundry products and fresh- air sprays often contain toxic chemicals and xenoestrogens that can cause and aggravate breathing problems and irritate skin.

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Again I want to stress that I personally I do not agree with the doom & gloom mongers who claim that it's reusing plastic bottles that's unsafe. My suggestion is that if it was safe to use in the first place, provided it is not damaged and is kept clean there is no reason to believe that it should be viewed as unsafe to reuse. Whether certain types of plastic are "safe" for food use in the first place is another matter.