Hi Oliver

you don 't need electroporation, I used fugene 6 Roche with 50% confluent cells (cells split the day before) and Optimem (Gibco), adding after 12-16 h 1 ml RPMI 10% serum (more o less). After 24h I get > 90% expession of a pGFP, as analysed by FACS.

Electroporation works better with non-adeherent cells, in my knowledge.

....sometime the low efficency depends from toxicity of the protein expressed, it happens if you are using a strong promoter such as Cytomegalovirus