– It can also help alot if you try to use short identifiers of css class names, element ID's, Javascript Functions, etc. Especially when u have large grids with lots of columns and rows.

– Check out the  "OptimizeCSSClassNamesOutput" property this does what i described directly from Infragistics, so the grid renders more Compact.

– Setting style/appearance property at top most level
We in our company make really heavy use from Infragistics Appearances in our Fatclient, and we had to port this to web. So pay attention how you build your Grid on the server side. Keep the defaults in mind and set the stuff on the server side only exactly when its needed. If you iterate through cells in the Webgrid on server and set some style/appearance properties, this will have a direct inpact to the html. Because then everycell has the style directly set (not through CSS identifiers). Never set any properties on a level where you can set a property on a parent level. (If the row itself has backcolor=red, avoid setting it on the cell) I know this sounds simple and clear but its very important to always keep this in mind. A wrong implemented appearance on server side can heavily destroy performance.
We get so far in our company that we created "CSS styled" appearance merge logic for infragistics appearances…