In its current iteration the Guild Store is absolutely useless. The reason being is because there is no refined and efficient way to use this feature.
If I want to search for a particular item I can't because there is no search feature. If I want to refine the items I am looking for I can't because there are not enough subcategories and many items get lumped into various categories. Finally due to the limited size of Guilds I can only sell to 500 people at most in each Guild, and if you figure in how many people actively play or would actually use the Guild Store in its current state that number begins to drop off from there.
Two things that need to happen:
1. A search function must be added as soon as possible, this is THE most important feature of ANY Auction House.
2. More subcategories are needed. This feature could be added later on if the search function is put in, but this needs to happen. Right now many of the items are in an uncategorized mess for the most part. One category you actually did a good job with is the Glyphs categories and this would be an excellent model to shape the entire Guild Store with.
I would really love to see the option of being able to buy from any guild store as well, but that is probably unlikely to happen since too many people would for some reason complain about having a bigger market.
Remember, you're unique... just like everyone else.
Characters
Tiberius Aulus