I have just upgraded from
Win98SE.
Here's a list of hardware for which XP rejected the drivers:
Fun, eh?
After a bit of fruitless tweaking, I opened the case and removed the offending modem and replaced it with another one I had on hand. The replacement modem would work with the generic driver from MS which allowed me to get online and get new(er) drivers for all the other hardware. I've yet to bother to put the case back together.
The god awful new user interface is very easily replaced with classic-style themes. Besides a couple supergroovy futuristic icons that I haven't gotten rid of yet, I've got the XP UI back to being more or less identical to what I had in 98SE. I did notice an inexplicable tendency to revert to the default Windows For Retards UI after taking off various useless eye candy effects. Provided you've saved your appearance settings, this is only a minor nuisance. Slightly more annoying was XP refusing to accept some of my old user settings during the upgrade. It would not accept an all numeric account name during the upgrade migration, though it made no objections about changing the name back after the installation was complete. It would, however, accept both the new and old user names during login, even though there was technically no longer any account associated with one of them. The start menu's "Log Off..." item also continued to display the temporary account name used during the upgrade. This was overcome by creating a new admin account with the desired name, logging in on the new account, and deleting the old admin account. If you have this account name problem, do it first, as you'll have to reset all the GUI options on the new account (of course if you saved you settings it only takes a few seconds). Remember to move all your user files over to the new account.
There are a couple disconcerting things about program conflicts. A number of plugins for Winamp give errors causing the application to forced quit. Work around this by moving the problematic DLLs from the winamp\plugins directory or by modifying the extension (E.G. *.DL_). It demands that I reinstall Nero, which I haven't yet done, but having read fondue's comments on Digital Rights Management, I have a suspicion it won't be as easy as just popping in the disc and clicking "OK." The creepiest occurrence was signing on to AOL and getting a message to the effect of "Ve know zhu have Veendoz Ecks Pee. Zhu must upgrad or ve vill hurt you." Not a problem, in so far as AOL disks are fairly ubiquitous (got one in the mail today, fortunately), but I did have to DL a 7.0 compatible version of some add-on software I have.
Besides the above I have no complaints. If there has been any change in performance it's in the way of improvement. I have an AMD K6 200Hz on this machine and it takes less than 2 minutes to boot (which is, may I add, an improvement over 98SE for this machine). I have not yet operated the machine under a normal/heavy program load, but I expect no problems.
In short, if you don't have a computer cobbled together from off-brand crap from the mid-90s, it will probably be a positive experience. Even if you do, it's relatively painless.