1) It seems to be better suited to a larger screen. I had to zoom it out a bit when viewing. The main page doesn't even fit on my laptop screen (1366x768 pixels). The menu is cut off at the bottom of the screen.
We did design the site for larger screens (1280 x XXX) but it should look okay on (1024 x 960) as well. We are working to make sure it looks okay on an iPads and tablets.
1) It would be cool if you could select more than one spec to be used to build the list of results (for instance if I wanted to see all rosewood bodied, GS guits, etc).
The reason you can only choose 1 filter (Shape, Wood, Series or Category) at a time is that it ensures there will always be at least one guitar in the results. If we allowed 2 filters (for example, a shape AND a wood) it would often return no results which is very frustrating to users. So we did the next best thing which is a sort of the results.
1) I wish string spacing info was included in the guitar specs (spacing @ nut, spacing @ saddle). I had a 314ce for a short while and now have a 714ce. The nut width is the same, but the string spacing is different. I think this is good info to have readily available, and it seems to be a frequently asked general question.
We will be adding more specs.
2) On a related note... I wish there was more information on the various neck profiles. There's plenty of info on the NT neck, but no info on the various neck styles. Standard vs Slim vs T5 vs other neck profiles. What are the differences, on what guits are they offered?, etc.
Interesting suggestion. I'll talk to our editor.
3) Some sort of compare feature would be nice.... like a little check boxes that can be selected and a main "compare" button someplace. This would allow direct comparison of a couple models.
This is on our wishlist as well.

2) I wish, when displaying the lists of results, they could have a selectable format (like small icons). This could allow many more guitars to be displayed on a single screen. There would be less pages to of results to click through.
Would allowing you to select the number of guitars to show per page work? For example a dropdown with 9,12,15,18,21 options?