The only practical issue I am aware of is that local accounts on one machine will have NTFS permissions on the others. This would definitely be an issue for clients, especially with worms spreading over admin shares, or just nosey clever people.
I've seen a number of Citrix MetaFrame servers at a previous workplace had the same SID - the Altiris tool hadn't been working right. These were maybe 20-odd HP blades, and had been in production for months. I'm not aware of any faults which could have been traced to the duplicated SIDs.
Names are another issue - your co-workers must be renaming machines or they couldn't join the domain.
Don't forget to clear out event logs and delete any system restore points before making the image.
Disadvantages of Sysprep on XP include all the new-user nonsense Microsoft litters the desktop and start menu with - media player icons, the windows tour, that $@%&!! search puppy... all this can be controlled with group policy, but I can understand why you would choose to avoid it altogether.
New user profile behaviour also changed with SP3 on XP, whether it was based on the Administrator's profile or not - more stress for those who already had a working deployment system prior to this.
Mini-setup on some ThinkPads (T61 and newer) can take like ten full minutes to finish setting up the network - this is time that could be better spent reading Server Fault.