I’m using Google Calendar, but not under my Gmail account. I use it under Google Apps service. Right now, if you use use Google Calendar under Gmail account, you should have a new look.
After signing-in, I was greeted with this message:

We’ve updated Google Calendar to make it more consistent with other Google Apps. Everything works the same as before, with one exception: we’ve removed the Tasks link. Now to turn tasks on and off, just click the Tasks calendar in your calendar list.

It’s more polished now. Look at the screenshot below (Click to enlarge)
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Now, let’s compare with the “old” one — Google Calendar design for Google Apps domain I’m having right now.

In most cases, Google Apps for domain service will have the same features (including design) with primary accounts under Google account. I think, I just need to wait. The new design looks better.