What is the current thinking on 4K Ultra High Definition TVs? 

When I last looked at them a year ago it seemed the consensus was that it was better to wait and maybe actually better to stick with a regular 1920x1080 Full High Definition TV instead.

I'm looking at getting a new TV that is somewhere around the 48" to 50" size - I really don't want to go any larger than that.  Should I be looking at UHD only at this point?  Should I sit on the sidelines a little longer?  I have a Samsung 40" LCD Series 6 that has treated me well the last 7 years, but I am thinking it is finally time to upgrade (and I'd like a slightly bigger screen as the 40" is feeling a little small for the room it is in).

Are Samsung and Sony still the leading brands to go with?

I guess I should ask if curved screen is worth the extra money?