[ic] items can't be removed, changed from cart; session questions

[NOW Website Coordinator]

Currently using: 5.0.1 with PostgreSQL and Linux

Customers are saying they can't delete items from the cart, and one said he 
couldn't change the number of the items.  I can't replicate this on IE or 
Firefox, although more have had this problem with Firefox (could be 
coincidence) .

I had one customer try another IC site, and he had a similar although not 
the same problem:

"Had not same problem (it not keeping a changed qty) but did have problem
with update button not recalculating (happened only once).
Also same problem of back button showing an Expired Page error."

He's using IE, has cookies on, etc. (not sure that cookies are still 
necessary, though for IC -- are they?)

My questions:

1) Does anyone else have these problems?  How have they solved them?

2) Which is better -- sessions in a DB or in files?  Does this matter for 
these problems?

Obviously, I could upgrade if it would matter but I didn't see anything in 
the changelog about this.

Thanks.