I wish I could ditch Windows. I would happily switch completely to Linux if it ran the applications I need, or equivalents, but it just doesn't.
First of all I need Quicken for my money. I tried some Linux apps that purport to manage your accounts but they're nowhere near as mature, they don't have the functions I use, and they're buggy. I could give up a few functions but buggy isn't acceptable when I'm dealing with money. Also, I rely on TurboxTax and I don't think there is a Linux equivalent to that.
Also, I'm addicted to Lord of the Rings Online, which doesn't run under wine.
Also, I make floor plans and some other types of drawings with Visio and I can't find a Linux app that even comes close. Actually, I don't like Visio much but it does the job and it doesn't run on Linux. Open Office Drawing is very simplistic by comparison and it's buggy. A viable alternative might be an http-based app (i.e., web accessed only) from Autodesk. I haven't checked that out yet.
Then there are a few web sites I need to use that require IE. I might be able to get them working with the right Firefox plugins but I haven't tried that yet.
Also, I'm using an online backup utility (Syncplicity) on my windows machine that seems to work ok. There doesn't seem to be a linux equivalent that's solid. Unbuntu One is promising but (in my opinion) it isn't ready for prime time yet and I don't want beta software handling my backups.
There's probably another thing or two I can't do with Linux that isn't coming to mind right now. Also, I haven't found Ubuntu to be as trouble-free compared to windows as the hype suggests. It's better but not perfect. For example it sure messed up my system and gave me some headaches when I upgraded from 9.04 to 10.04. And a couple of things that previously worked don't work any more. Also, it doesn't have a driver for my printer even though it's a common one (Canon 870). Hopefully these shortcomings will get less over time.
Of course there's a long list of advantages to Linux, which is why I use it whenever possible. But I wish these shortcomings would vanish.