Issues are down to minor ones now. Our UK server, I get absolutely no problems on, the USA one well, ping is a lot higher but just one or two lag spikes, nothing to worry about. Got some tweaks here if anyone is interested, we reckon they work:
You will need to locate the config_mp.cfg file and open it in Wordpad.
Find your Steam folder > steamapps > common > callofdutyblackops > players
Change the following to:
seta cl_maxpackets "100"
seta snaps "30"
seta com_maxfps "100" (still experimenting with this one) but pointless putting it any higher than your monitor refresh rate anyway cos that's all your eyes will see

Remember, you're looking for a stable uniform fps, you don't want to be all over the place. I've capped mine at 75, but it stays at 75.
seta clanName "" ... You can place certain special characters in here, for example in game, I can only have 6S but if I place it here, I can have =6S=
"seta r_multiGpu to 0 if you have one gfx card, or 1 if you have SLI/Crossfire
"seta r_multithreaded_device" to 1 if you have a multi core CPU
As FritOz has already mentioned, upping the maxrate server side from 5k to 25k really seemed to yield the best results.
Treyarch are also fixing favourites over the next few hours. I'm sure you've all spotted the obvious
