thinkpad T420 user here running archlinux.
i agree with none of these points, actually, except #1, which i wouldn't know about because i'm not using dual-mode graphics card.
"2. inability to use multiple monitors" < incorrect. i use a docking station with a dell u2711 hooked up to it. pressing fn+f7 switches correctly between external, internal, and external+internal with no problems.
"3. some ports being unusable" < incorrect. every port on my thinkpad is usable, including the ports on the docking station.
"4. audio glitches" < incorrect. my audio works better with my u2711 (via display-port audio) than it does over my macbook air (via display-port audio). why? because i can control the volume via the volume control via linux+pulse whereas OSX artificially restricts me -- it tells me i can't control the audio levels via mini-display port unless i'm using an apple display.
"5. hand patching required to keep the laptop stable" < incorrect? by this, do you mean updates? don't all OSs benefit from updates? if you mean configuration, udev (now systemd-tools) found everything correctly on my thinkpad on the first go. this was the case when i recently ran ubuntu 12.04 off of a flash drive as well.
"6. poor support for X11 even with simple intel integrated graphics" < incorrect. i have the intel HD3000 on my thinkpad, which runs everything pretty much the same way that my macbook air (with the intel3000) runs them. flash video at fullscreen with no tearing, etc (in fact, flash runs better on linux than it does on my macbook).
regarding battery life, i did have to do a bit of tinkering there. but that's because i'm a bit power-consumption obsessed. i used powertop to show me what needed fine tuning, then wrote a power management script that changes my computer's parameters depending on whether it's plugged in. the result: an idle 7w power consumption (with wi-fi on). that's roughly the same power consumption i get from the macbook air, which is an ULV chipset. battery life for windows on my T420 is ~10 hrs. with linux,...~12hrs.
"no competitively priced linux laptops"? my T420 was $1000 with a 2520M processor, 1600x900 resolution display, 160GB intel SATA 3 SSD, and 8GB of RAM.