It sounds like your phone is simply under heavy load. Apart from really light users, everyone will experience symptoms such as input delay on the keyboard at some point. But the last couple of official ICS builds for the G300 are not really markedly slower than GB, they just have more bugs, largely thanks to some bizarre choices by Huawei. The official Vodaphone builds will suffer from running short of RAM more frequently because of the extra branded crap they have running from startup by default.
If however, you've not got a bunch of extra downloaded apps running constantly, or a particular app is misbehaving (quite likely with Android), then yeah, you might have a hardware issue.
Kill the bee... and ultimately... you'll have nothing to spread on your toast — John Shuttleworth