I totally agree with most of the previously said, the Soviets did owe a lot of their operational capabilities to the equipment with largely American-made trucks and jeeps.
I don't know why they even used any of the Western-made tanks, most of their own material was much better suited for arfare on the Eastern front. However, since the Soviet airforce had so little decent planes they did appreciate the P-39 Airacobras that the USAAF sent over, since if was a better match against a Me-109 than a Yak was.
Luckily, they pulled off the large scale evacuation of industry during the German advance in 1941, otherwise they might have needed MUCH more help.
That and not Lend-Lease or german underestimates of Soviet industrial capabilities were the main factor in the economic struggle. Lend-Lease was a big and welcome addition, but not vital, the evacuation was both a wise decision and vital to the survival of the Red Army in 1941-42.