It would need to offer complete export functionality to trust it enough and use it.
Also it could use something like...
For some items like resistors, capacitors, diodes... it could be useful to have stored the diameter, space between leads, the form (0603 for example for smds), hFe for transistors...
allow user to enter some kind of product code from some big stores (digikey, farnell/newark, rs-online) and retrieve the product info from their pages... see if they have some api they'd be willing to give you access to like findchips dot com does.
have something to the form of :
bought from :
store name ... store's unique id for the item ... how many items bought .... price of purchase for the set .... 1/10/50/100 piece price at purchase ...
[ add batch ] - i may order the part from several stores, depending on promotions or price variations and minimum quantities - sometimes it's worth waiting 10 days to get stuff from US, other times it's better to get from Europe even if a few dollars more expensive.
this way when i want to order more parts, the system could do a comparative search at all the online stores it recognizes and suggest the cheapest store based on the number of parts user wants and the conditions of the user (give more weight to stores user favors).
As in.. maybe I need 35 capacitors which are:
1.1$ each on Farnell or 0.75$ if bought a minimum of 50....
1$ on Digikey or 0.8$ for 10+ ...
So now I have several options:
1. get 35 from Farnell : 1.1$ x 35 + 4$ shipping (3 day delivery) = 42.5
2. get 50 from Farnell : 0.75$ x 50 + 4$ shipping = 41.5
3. get 35 from Digikey : 0.8 x 35 + 20$ shipping (free for orders above $200) = 48$ (+ about 3% customs fees if order above 150$)
Obviously i'll get 50 capacitors from Farnell even if I need only 35. But that could change if Digikey had 0.5$ for 100+ and I'm ready to do a $200+ order to get free shipping on Digikey , which I had it happen to me before.