Two cents worth from a SketchUp newbie. It depends on what you really need to do, but it seems you can do 2D in SU quite well.
I'm a dyed in the wool Paint Shop Pro person. (2D from Corel, and you can download a trial from corel.com.) However -- and it's a big one -- the older versions such as 7.04 and 9 are much better if Ebay or some other entity has them. You might check my little offerings of exteriors on http://marlisepsp.tripod.com/ and fabulous interiors at http://www.jaddell.com. BTW, PSP is much less expensive than Adobe Photoshop and there are plenty of tuts online.
As for me, I'm going to be using both because it's so much faster and easier to do a 3D view from any angle in SU and then export it as a JPG to PSP for some extra cosmetics.
--Marlise