I'm about to buy a 350D with 18-55mm lense but am not sure whether to
go for the USM version or not. As far as I can tell the only way to get
the USM version in the UK is in the silver body kit from Jessops for
£700. Otherwise the non-USM is widely available for £600 upwards. Is
the USM version worth up to an extra £100? So far I've only handled
the non-USM version and was struck with its lightness, it almost felt
flimsy. I'll try and get my hands on the USM one in Jessops. I
understand the optics are identical so what other differences will I
notice in use?

Any advice gratefully received.

Thanks,
Geoff

If the optics are identical then there is no use whatsoever.  usm 'ultra
sonic motor' means quieter and faster focusing.  However i have non usm and
even shot sports events.  They aren't noisy either.  Save your money.