I bought a Maxtor 250 about three years ago and then a 300 about a year and a half ago. They both worked fine separately and together with my (PC) laptop. I added another Maxtor 300 about six months ago. This third Maxtor is OK separately; however, when daisy chained together performance drops significantly. All drives are connected by Firewire.
I bought the third Maxtor because the first one (250GB) began to be a bit noisy sometimes (however, it is still working OK). On getting the new 300GB drive, I immediately copied the contents of the old 250GB to the new 300GB. Copying required several hours. Curious about the slow speed, I tried various arrangements of the daisy chain - including swapping cables. I tried copying from the laptop to various drives as well. My conclusion was that the daisy chaining was the major part of the problem but that the new drive was a contributor. I contacted Maxtor but the various people I asked for help either did not understand, could not help or said that there was no problem.
I got a new laptop about two months ago and performance with the external drives seems better than with the old laptop but is still slow when using all three drives. Of course, now I've discarded all the notes about file copy times, arrangements, etc. The new laptop (HP/Compaq nw8240) has a built-in Firewire connection. With the old laptop (Compaq EVO610c) I was using a plug-in Firewire card.
My method of working with these externals is that I (now) normally have the older drives turned off unless specifically needed. It doesn't seem to matter whether I have all three drives turned on during startup or whether I simply turn on an additional drive later. On the other hand, I've learned not to turn on a second drive and then immediately turn on the third drive - must allow some time to pass until Windows XP picks up the second drive. Also, I think I had some problems when turning on a second drive while Photoshop was running.
Anyway, the external Maxtors have been OK for me but I'll probably get a different brand next time.