My experience:
Project:
Lazarus 0.9.29, Kubuntu 64bit, Qt 4.5
more than 10.000 lines,
more than 500 components on form (including menu items)
Compliled binary 12.1MB, after strip 4.8MB, after upx 1.2MB.
When executed, System Monitor shows 14.4MB allocated memory and 23.1MB of shared memory.
Executing is very fast, I click in File Manager (Krusader) and binary is started in one second.
Some time ago in Windows (32bit Vista) was binaries even little smaller, about 500kb after strip and upx, but I added many lines and components.
When I compile my project with GTK2, binary is about 14MB and 1.4MB after strip+upx.
When I add new code and components, final size is growing very slowly.
I think it's very good.
B.