Definitely pass. Comparable sets were around $600-$700 on Black Friday, and it's not rare to find such a deal today. Bookmark Slickdeals.net and wait for a good price, you can get either a much better set or a much cheaper set.
As for 720p, etc... the native resolution is 1366x768. All material will be displayed at this resolution. Non-1366x768 material is scaled to this resolution. 1080i/p requires 1080 vertical pixels, this set only has 768, so you lose a great amount of detail. You won't even get full quality from 720p, since it's going to be upscaled by the set. But that's really common for fixed-pixel HD TVs.
To clarify the technical features you were asking about, the specs list this:
Broadcast Format Supported:
1080i (HDTV),
480i (SDTV),
480p (EDTV),
576i,
720p (HDTV)
Broadcast Format Displayed:
480i (SDTV),
480p (EDTV),
768p
That means this TV set will display an image if the source is on the top list. But, no matter what the source is, it will only display one of the resolutions from the bottom list. E.g., 720p and 1080i will both be scaled to 768p, but 480i, 480p and 768p will all be displayed in their full glory. Since most HD sources are 720p or 1080i right now, the vaaaast majority of HD you'll see is going to be scaled to 768p. This resolution is ideal for a HTPC (home theatre PC), though.
In short: Save your money. Wait for a good deal, either getting a comparable set for cheaper or a much better set for the same price.