I've been having a similar dilemma, I'm really tempted by a 9800 pro. The way I've been thinking, when you look at the benches of something fairly next-gen like Far Cry running in max detail (which is really how the developers want people to play it), the FPS really aren't that high. Current top end hardware can only manage averages of ~40 - ~50 FPS with all the eye candy on (without AA/AF). So if games coming out pretty soon are gonna make top end cards work hard it makes me wonder how long I'll be able to enjoy playing games at their max gfx settings on current hardware. After all if you spend a load of money on a decent card you want to be able to turn everything up. Not such a problem if you upgrade every six months but most people have to think a bit farther ahead than that.
There was a comment made by one of the Splinter Cell programmers in a post on beyond3d who said they're currently thinking of skipping the shader 2.0 model all together for their next gen stuff and writing for model 3.0 instead, with backwards compatability in model 1.1. If this is typical of games in development then this doesn't look good for the longevity of current high end cards, even if they are a good buy right now.