I have been very lucky. I purchased the Speedtouch 330 when I first signed up with Virgin and have had no problems installing it on 2 PC's since then. I was aware of the VIA problems prior to purchase and had bookmarked a few links just in case I experienced problems but I didn't have any.
I am well aware though that many other people are experiencing these VIA/Speedtouch issues and have contributed to several threads including a recent one by chugby click here on this same issue.
I feel that the ISP's should make you aware of this potential problem and at the very least advise you how to find out if you have a VIA chipset prior to supplying the modem and maybe offer an alternative if you are likely to have problems. The Speedtouch isn't the only USB modem available after all.
As you say, PCI modems are not known to cause the same problems so you would think ISP's would offer these as an alternative, they tend to be cheaper in most cases too. When I was first signing up for ADSL, one of the providers did have the option of PCI or USB but this is unusual. I suppose a lot of people are not happy opening the case and the idea of Plug and Play is appealing.
I don't think it is fair to criticise the modem (as has been done in another thread on here) as it provides a very adequate connection for me and many others, but ISP's must be aware of the growing number of people experiencing this problem and offer an alternative.