The ui uses a plain text editor and cannot support how html text are copied in, there is an enhancement in EhP1 that supports some html text but we still see funny results when text is copy and pasted, please see the help below
http://help.sap.com/saphelp_crm700_ehp01/helpdata/en/2f/40132e6b094295af4523a0ef444897/frameset.htm
also there is a company qnovate.com that has a bolt on solution that we are investigating, looks to be a richer text solution.