First off, the Phenom is not a 'poor chip' by any stretch of the imagination. It isn't quite as fast as the equivalent Intel chip and that's pretty much it.
With encoding, yes Intel chips are currently faster, but the difference isn't significant at stock speeds.
Intel have a perceived reputation as being "much better" than AMD at the moment. In practice, the only significant difference crops up in overclocking and the performance differences that appear then. However, you have to remember that this is supposedly an overclockers' website (even though we do get people on here asking "how do I overclock my XYZ chip?") and that - for the past eighteen months - Intel has worn the overclocking crown.
There are some benefits to running a native quad core processor - those are typically reduced latency to RAM access, reduced power consumption, etc. - but the Phenom chip is pretty warm, anyway.
The first benefit mentioned is effectively circumvented by Intel's superior branch prediction algorithms.
However, I like to think of it as the difference between a Ford GT and a Lamborghini Gallardo: both are awesome, but the Lambo's engine does it without forced induction.
To answer your question directly (or rather, continue from the second paragraph), you won't have a problem with performance if you buy a Phenom, especially at stock.
If Tony aka BigToe's results with Phenom over on xtremesystems.org are consistent, then I will be all the more willing to buy Phenom when my upgrade comes. Were I not overclocking, I'd simply buy the cheapest quad core I could find. Customers like us cannot buy poor processors at this point in time. Enjoy it.