They also say they have no fair use policy, but this in their terms looks like one to me:
11.2 To ensure we offer all our customers the best possible service, we apply the following restrictions. We continuously monitor our networks to ensure that congestion is not occurring. If usage is such that it is significantly affecting service to other users we will instigate congestion control measures. Heavy-usage applications such as continuous Peer-to-Peer (P2P) file sharing, streaming video, binary downloads or other intensive uses are not acceptable. Where the Service has been deemed to have been used inappropriately or indeed illegally to the detriment of the overall Service, we reserve the right to take action against this account
I have also heard quite a few bad stories about them with regards to poor speeds, bad customer support, dns issues & pings @ 700ms plus. Having said that one or two people seem to be happy with them.
I believe they are ran by the same people that used to run V21, which sets the alarm bells off straight away.
At the end of the day they have no magic formula. They are simply reselling a BT Wholesale service. It has been proved time & time again that truly unlimited broadband is simply a pipe dream for a BT Wholesale IPStream Max product. Especially when sold so cheaply. What tends to happen with such ISPs after a while is either they go bust, they introduce traffic management or their customers suffer horrendous contention bring speeds down to dial up levels.
If anyone is lucky enough to get unlimited with good speeds/pings/peering etc from this lot then more power to you. Personally I would be very cautious of them.
Some good reading from plusnets website regarding unlimited. Not the biggest fan of plusnet, but they have this spot on:
http://www.plus.net/unlimited_broadband/