Get the Atrix 2 instead. I've owned the Samsung Infuse and though its not a bad phone, it does have its issues. The Atrix 2 is a much better built, solid phone and the curved body and ergonomics are far ahead of the oversized candybar of the Infuse. It's size can get in the way and the thin and flat body always gives the impression that you might split the phone in half in your pocket, even wearing cargo shorts, which is usually what I wear. The 4.5" to 4.3" difference is pretty minor, but the Atrix footprint is smaller and with the rounded curves, makes pocketability far better. The weight of the Infuse also makes it feel toyish.
I've owned three Samsung Super Amoled phones and this is more personal preference but I rather have more natural, warm colors than oversaturated, cold colors which make me nauseous. The gradation is pretty bad since when all the colors are oversaturated, you can't tell slight color changes since everything gets pretty strong and solid looking, which I guess some people are wowed by and like it, but not me. The blacks are super black and contrast is theoretically infinite, but in practice these things haven't really been a big deal in comparison to LCDs for me. The full RGB non-pentile LCD on the Atrix 2 has a higher resolution (960x540) which makes a far significant diffference over a .2" screen increase and the Super Amoled tech, and the LCD is top class with great viewing angles, contrast, and much more accurate color. Yeah there are bad 4.3" LCDs, like the HTC HD7 or Droid X panels, but this is a far different panel and not all 4.3" LCDs are created equal.
As far as updating the phones, there are too many variables to really say one is better than the other, but the Atrix 2 is a newer phone just released on the same week that ICS was announced and also has an OMAP4 chipset, in the same family as the Galaxy Nexus which will be the first to be released with ICS. There's also the fact that Google owns Motorola now, so there's even less red tape involved, and more incentive.
Also forgot to mention the camera and video. The Infuse probably takes better photos, but the Atrix 2 isn't that far behind. When it comes to video, its a wash between detail and smoothness. The Infuse has more detail, but the Atrix 2 is smoother and the exposure adjustment is first class. Best of all, which many manufacturers have neglected, is the audio capture quality, which is very good on the Atrix 2. The Infuse is about average in this respect. I'm also pretty sure that the Atrix 2 has a better speaker since the one on the Infuse isn't that great since Samsung is too obsessed with thinness. Good sounding MP3 ringtones are a no-go on the Infuse.
People also seem to be liking the new "not"-motoblur minimal skin and are less favorable of the older Touchwiz found on the Infuse (the newer Touchwiz is only on the Galaxy S II variants). There's also of course performance, which the Atrix 2 is much smoother with its dual-core and has even more potential to get faster once it gets updated and the Android OS can properly support dual-core. The Infuse isn't as smooth and still uses the RFS system (I think) which makes app launching lag ever so slightly. The OMAP4 is said to be quite battery efficient and the general consensus is very good battery life for the Atrix 2, so you arne't sacrificing anything to get a faster, dual-core handset.
Last but not least, the Atrix 2 has both a camera shutter button and an LED notification light hidden in the front, none of which the Infuse has.
Sorry I kind of went overboard since I am planning on getting the Atrix 2 and sold my Infuse a couple months ago. It's kind of weird that I am getting excited over a non-flagship, low-key, lower-priced phone, but many people are considering this a big sleeper hit. Hopefully it gets some success with a better marketing compaign or support may wane.