Yep. You are choosing the wrong time to switch. Generally speaking the Phenom II CPUs are basically on par with Intel's Core 2 Duo series. The FX (Bulldozer) series is basically considered to be a "side-grade" from Phenom II. In fact, many people here in the forum decided to buy a Phenom II over a FX CPU when they were holding off upgrading whatever AM3 CPU they were using.
Clock for clock, the 1st gen Core i3 is more powerful than a Phenom II / FX CPU. PileDriver is AMD's next CPU and AMD expect it to be about 10% more powerful than Bulldozer (FX). If that is true, then PileDriver will basically be equal to the 1st gen Core i3/i5/i7 CPUs. It is unknown if there will be a CPU after PileDriver (2012 thru 2013) in 2014. If there will be one, then it's unknown if it will use socket AM3+.
AMD has stated they will no longer compete directly with Intel. Arguably, you can say that AMD will stop producing consumer CPUs all together (they will still have server CPUs). They will focus on producing APUs, which are basically CPUs with graphic cores like Intel's Sandy Bridge and the upcoming Ivy Bridge CPUs.
The follow-up to PileDriver will be SteamRoller; however, so far any and all mentioning of SteamRoller has only been connected to AMD's APU processors (at least based on what I've been reading). Llano is AMD's 1st generation APU and it is socket FM1. Trinity is the 2nd gen APU which is based on the Bulldozer CPU core and it will be released this year. But it will be socket FM2, therefore it is not compatible with motherboards designed around socket FM1. Kaveri will be AMD's 3rd gen APU and will be released in 2013, but it is unknown what socket it will use.
So... from a CPU processing performance point of view, switching to a FX CPU right now is like taking a step back to Intel Core 2 Duo series. You need to wait for Piledriver CPUs to come out to get back on par with the 1st gen Core i3/i5/i7 CPUs. PileDriver is rumored to be released in Q3 2012.
If you feel that need a more performance, then I recommend you wait until the end of April for Ivy Bridge CPUs to come out. The performance increase over Sandy Bridge will be relatively small, but you might as wait for that little extra performance (likely to be on average 6% or 7% better with same clock speed in my opinion). Of course, if you think your current CPU is fine, then you can wait for Intel's Haswell CPU which is probably coming out in mid-2013.