Actually, I've done a couple, but they weren't my VFP apps. I did an eval for a company that makes some sort of help desk app in VFP, we tested 3.0, 5.0 and 6.0. 3.0 was pretty useless, besides the slowness by the overhead of the 16-bit compatibility code, the screen IO is pretty poor (lots of bitmaps and not real Windows controls). The same app recompiled in 5.0 was perfectly usable even over dialup connetions, and 6.0 was even faster. The test apps being run used native tables, but there really wouldn't be a difference if you used a SQL backend, at least not any different from a regular local app using the backend. It would be in almost all cases faster than having a VFP front end running accessing a SQL Server backend over a WAN link, assuming the Citrix server and SQl Server have a decent connection.
At other sites they had a laundry list of apps to run, and it turns out some were FPD, FPW, and VFP. FPW isn't too speedy, again it's all bitmaps and not real Windows controls, but on speedier links it worked well enough. Especially on the native tables, it was FAR FAR faster than it could ever be with the app in a remote site hooking to a shared drive over a WAN link.
In my experience (and I've been installing Citrix servers since WinView, the OS/2 version back in 94) I've found very few things that won't run. If it will run under NT, it generally works with Citrix. You don't want to do lots of graphics (Powerpoint, CAD, Visio) over it, but anything else is fair game. With the newest product, nFuse, you can set up an authenticated dynamic web site which will display icons for the applications each user is authorized for. The client uses a web browser. Pretty slick, and no visiting the desktops or trying to talk users through adding a new application, and no managing desktops through policies, each applicationt he user connects to runs that app and nothing else, they never see a desktop. It appears to the user that the app runs on their desktop.

Randy