As stated in the posts earlier, every usb compliant device should work without any problems at up to 5.25V. If your peripherals draw more current than the PSU can provide, or the board (due to polyfuses etc.) or cable causes a voltage drop - you either have to supply more power, or fix/bypass the cause/s (replace polyfuses, use better cable, stronger PSU, powered hub...).
Check voltage on TP1&TP2. Anything below 4.75V will most probably cause problems, because it will be even less for the usb devices (if you have the board with polyfuses).
So you cannot go wrong here... Once your board has trouble caused by low voltage (like mine), this is the easiest and safe way to go. Just try another -reliable PSU, or make your own
And get a solid usb cable.
Here is my temporary/testing construction: http://elinux.org/RPi_5V_PSU_construction
. I'm running it at 5.25V, but that's what the supply provides, TP1&TP2 say 4.82V. My plan for later is a (homemade) switched PSU with fine-tuned voltage and protection circuitry...