It's been a bit over two months since we've had any new realms for US players (the last new realms came with the release of the Burning Crusade on January 15th), there's been some cry on the forums for new realms to be opened. But with pre-BC server improvements helping overall realm stability and population cap increases limiting queue time, I haven't been seeing a lot of realm status complaints that would seem to justify the need for new realms or transfers. (My own realm has been pleasantly queue-free since BC's release.) CM Tseric seems to agree with this assessment, since in response to recent requests for new realms he's very clearly stated that there are no plans to open new realms at this time -- but that it's always under consideration, and they'll let you know when they'll be opening new realms.
However, my realm -- and the news I'm reading on the forums -- may not present an entirely accurate picture of how all the realms are behaving. So do we really need new realms to take some of the burden off overcrowded existing realms? If your realm is struggling, speak up and let us know!