yes the conroe has more actual power but it really doesn't matter. general applications you WILL NOT see a difference.
if you're running your average say episode of lost will you feel the difference between your task manager saying your athlon is using 25% and your conroe is using 15%? no. will firefox open a page faster? no. will games improve the fps so much that a higher resolution is available to you? no, and anyone that tells you the answer to any of those is yes is flat out lying to you.
if you have a x1900xtx and you play fear at say 1680x1050 with aa/af set to mid and its playable but 1920x1200 isn't, then going from a x2 3800+ to a c2d clocked to 3Ghz WILL NOT suddenly let you play at a higher resolution, it might give you 5fps more at the same resolution, if you're lucky. the other games that are cpu limited such as supreme commander also WILL NOT let you play at a higher res, its just the difference between playable or not.
there are a load of threads across multiple forums where people have a low end cpu and have lots of supreme commander problems, even people with really good graphics cards and what do they say, something along the lines of "i don't know whats wrong, even if i drop the resolution down to low settings i still don't get good framerates". its because the gfx can cope at higher fps, the cpu just can't do the calculations for all the units fast enough. those are the few games that yes, a conroe overclocked will show a difference compared to a lowly clocked cpu, but a dual core ath x2 won't show a huge difference either.
overall, be honest, everyone in this thread, name the most cpu intensive programs you use and how often you use them.
games - cpu isn't a big deal as long as you have really any dual core cpu, and 99% of games will still run on most single core cpu's the same.
video encoding, small sizes the difference won't be dramatic, re-encoding big files will show pretty big differences in times though.
you get the drift, other than gaming how many of us really use the cpu for anything cpu intensive?