I am trying to put a simple table of text (excel) into my layout and preserve cell formatting including alignment, borders and text sharpness. I've tried many approaches but nothing so far is satisfactory. BTW: ArcGIS 10.1
I discovered the solution to this by accident a couple of weeks ago. It's so simple it's almost too good to be true:
To ensure you don't get any jpeg jaggies use the same font size in Excel as you would in Arcmap if it were directly placed text from the Drawing toolbar. The table on this map was formatted entirely in Excel, using data-driven conditional formatting, detail below:
Limitations: The table is just a dumb graphic. If you see a spelling mistake or need to udpate it for next year you'll need to repeat everything (but that's the same for the native Arcmap embedded tables). To make repeated updates easier, export rather than copy the table (saving results in a model for quick repeat), and use saved styles and formatting rules everywhere possible in Excel.
I'm using ArcMap 10.1 and Excel 2010. It'd be interesting to hear if this a version specific thing or this has been around for awhile (and does this only work with MS Office?).
Have you been using the Online Help for Adding a table to a layout?
There's also quite a bit on getting the Appearance of the Table right, which you need to do before adding it to the layout, on the help for Understanding field properties, aliases, and table display options.