software is quite a broad topic....care to be more precise ?
I have bought software from ebay - as in games for pc and consoles.
i assume you are asking if it safe but at the end of the day its the sellers you need to be careful of ,not the products.
You only get what you pay for. If you get �100-worth of software for �5, don't be surpised if it's just a copied disk.
I've bought a handful of times, once some cheap stuff that I only needed for a one-off (yes, it was copied) and a couple of times I bought 'serious' software, for which I paid a reasonable/expected price and it seemed - to me - to be legit.
As Matt says, check the seller's other auctions and feedback - you can work out what sort of software you'll get!
I bought several copies of Nero plus all the plugins and a bundle of extras thrown in from ebay - the whole set cost �6. It was a perfectly legit OEM copy (original discs + serial numbers), the seller had 3000 positive feedback and clearly had plenty of these packages to sell.
I would normally be wary of this kind of offer but in this instance it proved a great deal.