Here are the direct links:
There are two main annoyances so far, one of these annoyances is that the optimizing images process takes a very long time when installing iOS4, the other problem is that performance on the iPhone 3G is said to be very poor.
This is probably because the iPhone 3G has just 128 MB eDRAM and a 620 MHz processor underclocked to 412 MHz, whereas the iPhone 3GS 256 MB eDRAM and a 833 MHz processor underclocked to 600 MHz.