I've got an E51 and an N800 and I think it has to be the greatest combo since peanut butter and jelly. I was previously using it with a $20 a month unlimited data plan (GPRS/EDGE only) and am on a similar plan with a different carrier. I wouldn't call it the fastest in the world, but its good for general web browsing and updating the various bits of software. I also have tested the Joikuspot application and it works as advertised, EDGE isn't great but its fast enough that my girlfriend and I were able to browse the web on the N800 and a laptop simultaneously. Since we don't live in New York we don't have T-Mobile 3G, and I don't know that the E51 could do it anyways (that's why I'll upgrade to an E71 if 3G ever gets here). All in all for the price I'm very happy with my E51 + N800 vs the E90 I could have gotten for the same money. I get the benefits of Linux and a touchscreen as well as Symbian for the same price I would have paid otherwise.

Everyone is probably aware of many of the things you can do with the N800, RDP to a windows server, VNC to a Linux one, I was able to SFTP to a storage server and monitor the progress of an upload from another remote computer. There are torrent clients, streaming radio, and even the Carman software for the gearheads (of which I'm not, but I luuuurve my gadgets).