I'll put my 2 cents in on Teracopy. I think it's an awesome product. Actually it got much better with their latest version. Before it was a little annoying at times but still worth it.
I've used it on both XP and Vista machines, and seen improvements on both, I think. Speaking of, I need to get it on the media computer at church - keep forgetting to do that.
Here are the things I really like about it from real world usage:
[ol][li]It's Free - unless you need the Pro version - I forget what benefits the Pro version adds[/li]
[li]Speed - it generally seems to transfer AS FAST or faster than Explorer - I think most of the time, mine have been at least somewhat faster, but I never took the time to test it, really.[/li]
[li]Information - You get LOADS of information telling you the speed of transfer, % complete, etc. You also can see a full report at the end verifying each file as completed or not - and it might tell why, I forget that too.[/li]
[li]Awesome Overwrite options. It sort of has the options that Windows Explorer Vista has, but oh so much more. For instance, when copying a folder, it doesn't bother just askign if you want to overwrite the folder. No, it goes strait to the files - "Do you want to overwrite file1?... you can rename, copy anyway, or skip... and you can choose "All" for any of the options[/li][/ol]
My opinion, hands down, I wouldn't want to do a file transfer THAT large without TeraCopy or something similar. I've not used all the competitor's ones. I might have tried one or two, but I haven't had many free applications leave quite the impression that TeraCopy left on me.
Now for the annoyances. There are no ads or any of that garbage with it, so that's a plus. Actually, in my opinion, it's kinda hard to see who made it or what their website is when you're running it - you have to work for that, which IMHO is a good thing.
But there are some issues which were mostly taken care of in the current version.
First, it used to be the case that if you started one REALLY big transfer, and wanted to do a small transfer in the mean time, you'd have to cancel the first!! So, say you've got the 2TB transfer going, but need to quickly send out a 45KB document to a USB thumb drive in the mean time. In the old version, you just couldn't. It would get in line behind all the others. The new one seems to mostly get around that by having a separate process/prompt show up for each transfer. If it's a large transfer, it'll say something to the extent "waiting for other process to finish"; if it's a small file, it'll go ahead and move it for you. So really, it's mostly fixed that whole issue.
I can't really think of any other headaches with it, honestly. That one headache was driving me bonkers for a while.
Oh, one other minor issue - also already fixed, and it was more on the AV side. AVG 8, when it first came out, would flag TeraCopy as a virus, and remove the application! Even if you tried to add an exception AVG would end up freezing the program. Then guess what, no way you were moving a THING on your computer without uninstalling TeraCopy. Thankfully within a week or two of my having that issue, it seemed AVG got their act together on that app.
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"If to err is human, then I must be some kind of human!" -Me