I don't notice a large acute strength gain immediately, but by days 10-14 I start to notice a slight increase in strength and a larger increase in overall work capacity (in the form of greater overall volume/reps).
WHAT THE SCIENCE SAYS:
http://www.ncbi.nlm.nih.gov/pubmed/23035701
16 resistance trained men, given 750mg of PA vs placebo assessed for strength (1 RM) during each training session exhibited:
A. 12.7% increase in squat strength (vs 9.3% for placebo)
B. 2.6% increase in LBM (vs 0.1% placebo)
Larger doses of PA may lead to greater gains in all measurable areas based on private conversations with the scientists behind the study and also demonstrated through a large amount of anecdotal data.
P.S. If strength is your goal I'd give Tr1umph a look as well. There are multiple ingredients in addition to SL/PA that are proven to increase max power output. We're having some large sales March 2-10.