My experience
I've had ADSL for the past 6 years, 5 years of those with Zen. I've used a DLink DSL504 up till 2 months ago when I switched to a Netgear DG834G v3. My first year of ADSL was with BT Openworld and I had nothing but trouble with the connection, several things were tried but eventually I switched over to Zen when my 1yr contract was up. The service improved dramatically and I had no problems until I switched to ADSL MAX just over 2 years ago.
The Dlink started disconnecting twice a day (so I bought the Netgear - same trouble) and I had real difficulties getting the connection back up involving a full power cycle of the router. I have a dedicated line for ADSL hanging off the master socket with a faceplate. No external filters, no extra devices. According to my research neither of these modems have the faulty chipset in question which leaves me in serious doubt as to the credibility of this claim.
Biting the hand that feeds IT
