This thread is childish. I used BitInstant for my first time a few weeks ago and I experienced a smooth transaction with zero confusion using BitInstant's simple interface. I used Dwolla to purchase BTC sent directly to a wallet address and received them within 5-10 minutes.
The title of this thread should be changed. Website design is not poor; it's about as clear and simple as you can get given that every time you change your payment method or target destination, the website automatically refreshes to reflect the change.
Now, let's say you choose "BitStamp" as your destination account. The website will show three fields: one to enter "Account ID or Username," one for "Amount (USD) to Pay," and one for your "Notification Email." If instead you choose something like "Mt. Gox" for your target destination, you will notice the top field has changed from "Account ID or Username" to "MtGox Account #." This should make it extremely obvious that the account ID BitInstant was requesting for your transaction was a BitStamp ID, not a MtGox ID.
To demonstrate the point further, select any of the target destinations, but then cycle through the different funding options. You will notice that no matter what funding option you pick, (MtGox, Dwolla, BTC-e coupon, etc.) the text fields now remain exactly the same. This should make it even more obvious that the account ID requested will ALWAYS be that of the target destination and not the funding option.
My guess is that if the OP had taken even 5-10 more seconds to look at the site, he would have solved his own confusion. Now, please change the title of this thread.
Website design is about what the user experience, and that was my experience when I first started to use it.
You've only addressed one issue, if you look at the other issues I've stated, you'll know what I mean by poor design.
Look at all the other complaints too, it's not like I am the only one having the problem.
I haven't been really using the site since.