I've been doing this for about 10 years (detailed here in my journal). I had about $50k at one point. I am now doing something I call "hot potato", though I am sure there is a name already for it...in which I do BT's on cards with fee-free BT's at the same rate as purchases...and I just transfer it to another card before interest can accrue. I was able to roll around $5k of expenses around, until I recently paid it off with a 0% transfer offer for 16 months. Which is good, because I was running low on the limit of one of my cards, so the clear slate will allow me bounce around more expenses. I try to spend credit/save cash, as much as possible.
The "hot potato" is a good way to stall while waiting for an existing card to offer a 0% promotion. It's also nice to have an available wad of debt available to take full advantage of special offers, so I don't have to go hunting and pecking for ways to incur beneficial debt (like servicing my car or having to buy gift cards to grocery stores, or phone cards, etc).