The 4" Makita (model 9403 here in Europe) is an absolute beast. Yeah - it's heavy and built like a tank - but I can't think of anything I'd rather use to remove maximum amounts of stock in minimal time. The weight of the machine is quite often a big advantage for applications like floor or table-top sanding, because all you have to do is to hang onto it and let it do its job - there's no effort needed at all. I also use mine on its side very frequently, however - putting a radius on the corner of a countertop for example, so the weight isn't crippling. An additional plus is that the onboard blower is very effective, meaning that you can quite feasibly use it with the supplied bag without throwing dust everywhere. For bigger jobs involving hookup to an extractor, you'll need to source a hose adaptor, since Makita have their own wacky ideas on how big a port should be. If this is the case - I'll take a picture of mine and show you the dimensions you'll need, if that would help.
If you decide to go down this route, I'd also recommend that you get a couple of replacement graphite pads (Makita part number 421648-9) which cushion the baseplate from the belt. They're cheap to buy, quick to fit, and do a great job at drastically reducing the belt/baseplate friction which makes the lower half of the machine heat up as you use it. Although they're pretty durable, it's a wear item, and it's worthwhile having at least one spare. One final point to mention is that (in the UK, anyway) it doesn't come with a case, so you'll need the correct-sized Makpac (a Type 3) with the correct insert (Makita part number 837652-2), or put it in suitably-sized Systainer.
Oh - and if your car ever has a dead battery, put a 40-grit belt on the sander, hook it up to an extension cord, and fix a towrope to the handle. It will drag your car right along so you can tow-start it.
