DNS powers the web and quite often is the first service to fail on ISPs. Sadly this has been happening with O2 Broadband via 184.108.40.206 and as such I've resorted to making use of OpenDNS.
If you'd prefer to not setup the DNS entries manually on each client ( current settings are 220.127.116.11 and 18.104.22.168 ) then you'll need to use the following for the Thompson supplied O2 routers 1 2.
telnet 192.168.1.254 Login name: SuperUser Password: O2Br0ad64nd dns server route flush dns server route add dns=22.214.171.124 metric=0 intf=O2_ADSL2plus dns server route add dns=126.96.36.199 metric=0 intf=O2_ADSL2plus dns server route list saveall
Open DNS does seem to be a lot more reliable than O2's DNS making for a much happier, speedier and reliable connection.