I think the important thing WillC, is how much water you add when it is time to water.
I only keep bog plants and succulents in pots without drain holes becasue I know I can drown the papyrus and peace lillies, and the succulents will tolerate it when I only add a drop. Otherwise it requires too much vigilance for my taste.
The good news is you can drill holes in pretty much anything with the right drill bit and patience, but the bits for glass and porcelain are expensive and dull quickly. You're better off just buying a pot with holes.
