I personally got interested in Maemo by getting an N800 through a developer device discount. I like my N800, as well as my new N900. I don't, however, have any complaint that Nokia hasn't made Maemo 5 work on the N800; among other things, how do you expect to get a UI heavily dependent on graphical effects and compositing to work on a device with hardly any graphics acceleration for those things?

As Texrat said, take a look at Mer; it tries to create an OS based on parts of Maemo 5 that will work on many devices, including the N800 and N810. Furthermore, Mer has some community building up around it.