So we are losing two high definition broadcasters as they become one. The parent companies of UPN and WB, CBS and Warner Brothers, have announced they will form a new network with programming from both of the old ones, which will cease broadcasting in September of this year. The station will be broadcast on the Tribune's 16 major market television stations, as well as 12 CBS-owned affiliates. If you don't live in the 48% of the US that covers, don't worry, they will select existing UPN or WB affiliates throughout the rest of the country.
In the press release for the 10-year agreement, there is no mention of high definition, but since both existing stations currently broadcast some content in high def, it's safe to say the new one will as well.
Hopefully now they'll be able to broadcast in 1080i every night, instead of taking nights off as they sometimes have.